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 $57.51   7.793%   $61.9918   $61.99   $62.00   $62.00  
  Purchase #2 $20.30   7.353%   $21.7927   $21.79   $21.80   $21.80  
  Purchase #3 $135.34   4.344%   $141.2192   $141.22   $141.20   $141.20  
  Purchase #4 $214.87   4.555%   $224.6573   $224.66   $224.65   $224.70  
  Purchase #5 $117.71   5.664%   $124.3771   $124.38   $124.40   $124.40  
  Purchase #6 $112.38   13.702%   $127.7783   $127.78   $127.80   $127.80  
  Purchase #7 $45.84   4.760%   $48.022   $48.02   $48.00   $48.00  
  7 purchase totals = $703.95       $749.8384   $749.84   $749.85   $749.90