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 $59.35   9.380%   $64.917   $64.92   $64.90   $64.90  
  Purchase #2 $54.78   13.672%   $62.2695   $62.27   $62.25   $62.30  
  Purchase #3 $155.96   4.290%   $162.6507   $162.65   $162.65   $162.70  
  Purchase #4 $249.32   8.273%   $269.9462   $269.95   $269.95   $269.90  
  Purchase #5 $188.47   6.270%   $200.2871   $200.29   $200.30   $200.30  
  Purchase #6 $138.99   3.142%   $143.3571   $143.36   $143.35   $143.40  
  Purchase #7 $79.46   11.131%   $88.3047   $88.30   $88.30   $88.30  
  7 purchase totals = $926.33       $991.7323   $991.74   $991.70   $991.80