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 $186.96   10.730%   $207.0208   $207.02   $207.00   $207.00  
  Purchase #2 $201.31   12.581%   $226.6368   $226.64   $226.65   $226.60  
  Purchase #3 $40.39   13.271%   $45.7502   $45.75   $45.75   $45.80  
  Purchase #4 $201.98   13.134%   $228.5081   $228.51   $228.50   $228.50  
  Purchase #5 $249.95   7.213%   $267.9789   $267.98   $268.00   $268.00  
  Purchase #6 $119.50   13.583%   $135.7317   $135.73   $135.75   $135.70  
  Purchase #7 $126.65   10.652%   $140.1408   $140.14   $140.15   $140.10  
  7 purchase totals = $1,126.74       $1,251.7673   $1,251.77   $1,251.80   $1,251.70