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 $87.42   8.328%   $94.7003   $94.70   $94.70   $94.70  
  Purchase #2 $24.63   5.514%   $25.9881   $25.99   $26.00   $26.00  
  Purchase #3 $245.73   13.483%   $278.8618   $278.86   $278.85   $278.90  
  Purchase #4 $40.31   3.771%   $41.8301   $41.83   $41.85   $41.80  
  Purchase #5 $142.28   8.452%   $154.3055   $154.31   $154.30   $154.30  
  Purchase #6 $93.58   13.306%   $106.0318   $106.03   $106.05   $106.00  
  Purchase #7 $206.47   12.318%   $231.903   $231.90   $231.90   $231.90  
  7 purchase totals = $840.42       $933.6206   $933.62   $933.65   $933.60