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 $64.45   7.504%   $69.2863   $69.29   $69.30   $69.30  
  Purchase #2 $245.99   12.827%   $277.5431   $277.54   $277.55   $277.50  
  Purchase #3 $239.34   13.370%   $271.3398   $271.34   $271.35   $271.30  
  Purchase #4 $208.44   6.745%   $222.4993   $222.50   $222.50   $222.50  
  Purchase #5 $19.54   4.604%   $20.4396   $20.44   $20.45   $20.40  
  Purchase #6 $63.35   3.669%   $65.6743   $65.67   $65.65   $65.70  
  Purchase #7 $161.62   13.531%   $183.4888   $183.49   $183.50   $183.50  
  7 purchase totals = $1,002.73       $1,110.2712   $1,110.27   $1,110.30   $1,110.20