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 $72.53   7.559%   $78.0125   $78.01   $78.00   $78.00  
  Purchase #2 $187.73   11.741%   $209.7714   $209.77   $209.75   $209.80  
  Purchase #3 $96.55   6.873%   $103.1859   $103.19   $103.20   $103.20  
  Purchase #4 $208.77   7.560%   $224.553   $224.55   $224.55   $224.60  
  Purchase #5 $28.32   3.201%   $29.2265   $29.23   $29.25   $29.20  
  Purchase #6 $86.56   6.688%   $92.3491   $92.35   $92.35   $92.30  
  Purchase #7 $224.99   6.288%   $239.1374   $239.14   $239.15   $239.10  
  7 purchase totals = $905.45       $976.2358   $976.24   $976.25   $976.20