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 $190.39   13.112%   $215.3539   $215.35   $215.35   $215.40  
  Purchase #2 $15.96   4.483%   $16.6755   $16.68   $16.70   $16.70  
  Purchase #3 $58.45   4.115%   $60.8552   $60.86   $60.85   $60.90  
  Purchase #4 $138.54   4.756%   $145.129   $145.13   $145.15   $145.10  
  Purchase #5 $204.45   9.647%   $224.1733   $224.17   $224.15   $224.20  
  Purchase #6 $5.93   6.526%   $6.317   $6.32   $6.30   $6.30  
  Purchase #7 $146.26   13.384%   $165.8354   $165.84   $165.85   $165.80  
  7 purchase totals = $759.98       $834.3393   $834.35   $834.35   $834.40