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 $191.46   8.231%   $207.2191   $207.22   $207.20   $207.20  
  Purchase #2 $153.50   3.408%   $158.7313   $158.73   $158.75   $158.70  
  Purchase #3 $51.36   9.713%   $56.3486   $56.35   $56.35   $56.30  
  Purchase #4 $79.43   6.742%   $84.7852   $84.79   $84.80   $84.80  
  Purchase #5 $119.85   3.404%   $123.9297   $123.93   $123.95   $123.90  
  Purchase #6 $210.46   11.259%   $234.1557   $234.16   $234.15   $234.20  
  Purchase #7 $188.39   12.259%   $211.4847   $211.48   $211.50   $211.50  
  7 purchase totals = $994.45       $1,076.6543   $1,076.66   $1,076.70   $1,076.60