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 $118.62   6.855%   $126.7514   $126.75   $126.75   $126.80  
  Purchase #2 $36.99   7.196%   $39.6518   $39.65   $39.65   $39.70  
  Purchase #3 $73.54   7.742%   $79.2335   $79.23   $79.25   $79.20  
  Purchase #4 $180.92   8.317%   $195.9671   $195.97   $195.95   $196.00  
  Purchase #5 $108.63   11.611%   $121.243   $121.24   $121.25   $121.20  
  Purchase #6 $11.45   13.336%   $12.977   $12.98   $13.00   $13.00  
  Purchase #7 $233.73   10.567%   $258.4282   $258.43   $258.45   $258.40  
  7 purchase totals = $763.88       $834.2520   $834.25   $834.30   $834.30