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 $58.65   13.315%   $66.4592   $66.46   $66.45   $66.50  
  Purchase #2 $177.41   11.552%   $197.9044   $197.90   $197.90   $197.90  
  Purchase #3 $103.29   12.870%   $116.5834   $116.58   $116.60   $116.60  
  Purchase #4 $232.53   10.682%   $257.3689   $257.37   $257.35   $257.40  
  Purchase #5 $118.86   4.712%   $124.4607   $124.46   $124.45   $124.50  
  Purchase #6 $234.97   3.735%   $243.7461   $243.75   $243.75   $243.70  
  Purchase #7 $42.82   7.228%   $45.915   $45.92   $45.90   $45.90  
  7 purchase totals = $968.53       $1,052.4377   $1,052.44   $1,052.40   $1,052.50