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 $123.95   8.716%   $134.7535   $134.75   $134.75   $134.80  
  Purchase #2 $88.50   8.397%   $95.9313   $95.93   $95.95   $95.90  
  Purchase #3 $43.86   6.758%   $46.8241   $46.82   $46.80   $46.80  
  Purchase #4 $234.35   7.335%   $251.5396   $251.54   $251.55   $251.50  
  Purchase #5 $72.89   5.770%   $77.0958   $77.10   $77.10   $77.10  
  Purchase #6 $43.28   11.698%   $48.3429   $48.34   $48.35   $48.30  
  Purchase #7 $69.68   5.632%   $73.6044   $73.60   $73.60   $73.60  
  7 purchase totals = $676.51       $728.0916   $728.08   $728.10   $728.00