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 $86.69   13.662%   $98.5336   $98.53   $98.55   $98.50  
  Purchase #2 $209.76   9.541%   $229.7732   $229.77   $229.75   $229.80  
  Purchase #3 $82.86   11.121%   $92.0749   $92.07   $92.05   $92.10  
  Purchase #4 $150.85   8.746%   $164.0433   $164.04   $164.05   $164.00  
  Purchase #5 $127.41   5.681%   $134.6482   $134.65   $134.65   $134.60  
  Purchase #6 $181.95   9.222%   $198.7294   $198.73   $198.75   $198.70  
  Purchase #7 $50.89   5.619%   $53.7495   $53.75   $53.75   $53.70  
  7 purchase totals = $890.41       $971.5521   $971.54   $971.55   $971.40