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 $161.62   3.710%   $167.6161   $167.62   $167.60   $167.60  
  Purchase #2 $206.92   8.434%   $224.3716   $224.37   $224.35   $224.40  
  Purchase #3 $98.85   3.394%   $102.205   $102.21   $102.20   $102.20  
  Purchase #4 $62.34   11.742%   $69.66   $69.66   $69.65   $69.70  
  Purchase #5 $116.56   8.291%   $126.224   $126.22   $126.20   $126.20  
  Purchase #6 $185.29   11.707%   $206.9819   $206.98   $207.00   $207.00  
  Purchase #7 $42.97   12.719%   $48.4354   $48.44   $48.45   $48.40  
  7 purchase totals = $874.55       $945.4940   $945.50   $945.45   $945.50