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 $54.97   7.292%   $58.9784   $58.98   $59.00   $59.00  
  Purchase #2 $65.28   7.164%   $69.9567   $69.96   $69.95   $70.00  
  Purchase #3 $212.47   6.662%   $226.6248   $226.62   $226.60   $226.60  
  Purchase #4 $33.25   13.551%   $37.7557   $37.76   $37.75   $37.80  
  Purchase #5 $74.47   3.733%   $77.25   $77.25   $77.25   $77.30  
  Purchase #6 $121.98   13.515%   $138.4656   $138.47   $138.45   $138.50  
  Purchase #7 $99.28   13.403%   $112.5865   $112.59   $112.60   $112.60  
  7 purchase totals = $661.70       $721.6177   $721.63   $721.60   $721.80