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 $60.34   11.342%   $67.1838   $67.18   $67.20   $67.20  
  Purchase #2 $165.90   10.569%   $183.434   $183.43   $183.45   $183.40  
  Purchase #3 $205.30   10.569%   $226.9982   $227.00   $227.00   $227.00  
  Purchase #4 $101.55   4.566%   $106.1868   $106.19   $106.20   $106.20  
  Purchase #5 $105.37   4.842%   $110.472   $110.47   $110.45   $110.50  
  Purchase #6 $18.60   5.784%   $19.6758   $19.68   $19.70   $19.70  
  Purchase #7 $207.73   6.514%   $221.2615   $221.26   $221.25   $221.30  
  7 purchase totals = $864.79       $935.2121   $935.21   $935.25   $935.30