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 $22.68   13.374%   $25.7132   $25.71   $25.70   $25.70  
  Purchase #2 $115.86   8.199%   $125.3594   $125.36   $125.35   $125.40  
  Purchase #3 $105.84   10.578%   $117.0358   $117.04   $117.05   $117.00  
  Purchase #4 $236.26   3.146%   $243.6927   $243.69   $243.70   $243.70  
  Purchase #5 $106.58   10.558%   $117.8327   $117.83   $117.85   $117.80  
  Purchase #6 $76.29   9.575%   $83.5948   $83.59   $83.60   $83.60  
  Purchase #7 $105.86   13.299%   $119.9383   $119.94   $119.95   $119.90  
  7 purchase totals = $769.37       $833.1669   $833.16   $833.20   $833.10