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 $113.91   10.258%   $125.5949   $125.59   $125.60   $125.60  
  Purchase #2 $93.31   5.585%   $98.5214   $98.52   $98.50   $98.50  
  Purchase #3 $182.94   7.234%   $196.1739   $196.17   $196.15   $196.20  
  Purchase #4 $26.25   9.587%   $28.7666   $28.77   $28.75   $28.80  
  Purchase #5 $174.27   5.664%   $184.1407   $184.14   $184.15   $184.10  
  Purchase #6 $200.92   11.869%   $224.7672   $224.77   $224.75   $224.80  
  Purchase #7 $249.46   10.242%   $275.0097   $275.01   $275.00   $275.00  
  7 purchase totals = $1,041.06       $1,132.9744   $1,132.97   $1,132.90   $1,133.00