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 $84.79   9.377%   $92.7408   $92.74   $92.75   $92.70  
  Purchase #2 $131.26   3.585%   $135.9657   $135.97   $135.95   $136.00  
  Purchase #3 $229.62   6.303%   $244.0929   $244.09   $244.10   $244.10  
  Purchase #4 $59.29   10.315%   $65.4058   $65.41   $65.40   $65.40  
  Purchase #5 $26.56   7.130%   $28.4537   $28.45   $28.45   $28.50  
  Purchase #6 $9.45   5.462%   $9.9662   $9.97   $9.95   $10.00  
  Purchase #7 $141.42   7.400%   $151.8851   $151.89   $151.90   $151.90  
  7 purchase totals = $682.39       $728.5102   $728.52   $728.50   $728.60