Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $209.25   12.604%   $235.6239   $235.62   $235.60   $235.60  
  Purchase #2 $143.57   10.561%   $158.7324   $158.73   $158.75   $158.70  
  Purchase #3 $250.31   11.691%   $279.5737   $279.57   $279.55   $279.60  
  Purchase #4 $208.58   12.841%   $235.3638   $235.36   $235.35   $235.40  
  Purchase #5 $140.29   12.184%   $157.3829   $157.38   $157.40   $157.40  
  Purchase #6 $123.82   5.165%   $130.2153   $130.22   $130.20   $130.20  
  Purchase #7 $158.50   11.558%   $176.8194   $176.82   $176.80   $176.80  
  7 purchase totals = $1,234.32       $1,373.7114   $1,373.70   $1,373.65   $1,373.70