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 $89.36   6.730%   $95.3739   $95.37   $95.35   $95.40  
  Purchase #2 $215.49   4.815%   $225.8658   $225.87   $225.85   $225.90  
  Purchase #3 $104.29   3.281%   $107.7118   $107.71   $107.70   $107.70  
  Purchase #4 $224.88   9.214%   $245.6004   $245.60   $245.60   $245.60  
  Purchase #5 $56.91   12.581%   $64.0698   $64.07   $64.05   $64.10  
  Purchase #6 $28.50   8.572%   $30.943   $30.94   $30.95   $30.90  
  Purchase #7 $21.58   4.187%   $22.4836   $22.48   $22.50   $22.50  
  7 purchase totals = $741.01       $792.0483   $792.04   $792.00   $792.10