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 $30.63   8.290%   $33.1692   $33.17   $33.15   $33.20  
  Purchase #2 $231.37   12.656%   $260.6522   $260.65   $260.65   $260.70  
  Purchase #3 $53.57   9.146%   $58.4695   $58.47   $58.45   $58.50  
  Purchase #4 $204.37   11.222%   $227.3044   $227.30   $227.30   $227.30  
  Purchase #5 $69.79   4.258%   $72.7617   $72.76   $72.75   $72.80  
  Purchase #6 $192.43   3.158%   $198.5069   $198.51   $198.50   $198.50  
  Purchase #7 $230.71   13.302%   $261.399   $261.40   $261.40   $261.40  
  7 purchase totals = $1,012.87       $1,112.2629   $1,112.26   $1,112.20   $1,112.40