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 $55.71   11.260%   $61.9829   $61.98   $62.00   $62.00  
  Purchase #2 $45.56   7.413%   $48.9374   $48.94   $48.95   $48.90  
  Purchase #3 $37.44   3.488%   $38.7459   $38.75   $38.75   $38.70  
  Purchase #4 $54.35   13.214%   $61.5318   $61.53   $61.55   $61.50  
  Purchase #5 $104.53   13.157%   $118.283   $118.28   $118.30   $118.30  
  Purchase #6 $211.96   6.588%   $225.9239   $225.92   $225.90   $225.90  
  Purchase #7 $177.95   8.704%   $193.4388   $193.44   $193.45   $193.40  
  7 purchase totals = $687.50       $748.8437   $748.84   $748.90   $748.70