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 $58.75   10.234%   $64.7625   $64.76   $64.75   $64.80  
  Purchase #2 $106.54   9.731%   $116.9074   $116.91   $116.90   $116.90  
  Purchase #3 $248.27   9.625%   $272.166   $272.17   $272.15   $272.20  
  Purchase #4 $65.53   3.465%   $67.8006   $67.80   $67.80   $67.80  
  Purchase #5 $215.37   9.751%   $236.3707   $236.37   $236.35   $236.40  
  Purchase #6 $229.71   10.271%   $253.3035   $253.30   $253.30   $253.30  
  Purchase #7 $43.46   10.556%   $48.0476   $48.05   $48.05   $48.00  
  7 purchase totals = $967.63       $1,059.3583   $1,059.36   $1,059.30   $1,059.40