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 $57.75   12.537%   $64.9901   $64.99   $65.00   $65.00  
  Purchase #2 $131.26   12.485%   $147.6478   $147.65   $147.65   $147.60  
  Purchase #3 $17.40   8.439%   $18.8684   $18.87   $18.85   $18.90  
  Purchase #4 $174.65   3.308%   $180.4274   $180.43   $180.45   $180.40  
  Purchase #5 $207.90   13.361%   $235.6775   $235.68   $235.70   $235.70  
  Purchase #6 $118.81   11.795%   $132.8236   $132.82   $132.80   $132.80  
  Purchase #7 $24.88   9.616%   $27.2725   $27.27   $27.25   $27.30  
  7 purchase totals = $732.65       $807.7073   $807.71   $807.70   $807.70