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 $163.54   4.695%   $171.2182   $171.22   $171.20   $171.20  
  Purchase #2 $48.36   3.669%   $50.1343   $50.13   $50.15   $50.10  
  Purchase #3 $37.39   9.844%   $41.0707   $41.07   $41.05   $41.10  
  Purchase #4 $65.52   4.444%   $68.4317   $68.43   $68.45   $68.40  
  Purchase #5 $12.38   8.557%   $13.4394   $13.44   $13.45   $13.40  
  Purchase #6 $101.98   10.676%   $112.8674   $112.87   $112.85   $112.90  
  Purchase #7 $157.94   12.326%   $177.4077   $177.41   $177.40   $177.40  
  7 purchase totals = $587.11       $634.5694   $634.57   $634.55   $634.50