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 $226.95   8.344%   $245.8867   $245.89   $245.90   $245.90  
  Purchase #2 $82.39   12.323%   $92.5429   $92.54   $92.55   $92.50  
  Purchase #3 $25.74   10.223%   $28.3714   $28.37   $28.35   $28.40  
  Purchase #4 $98.75   8.824%   $107.4637   $107.46   $107.45   $107.50  
  Purchase #5 $190.50   6.162%   $202.2386   $202.24   $202.25   $202.20  
  Purchase #6 $59.47   10.840%   $65.9165   $65.92   $65.90   $65.90  
  Purchase #7 $232.64   8.742%   $252.9774   $252.98   $253.00   $253.00  
  7 purchase totals = $916.44       $995.3972   $995.40   $995.40   $995.40