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 $174.58   13.703%   $198.5027   $198.50   $198.50   $198.50  
  Purchase #2 $194.92   11.462%   $217.2617   $217.26   $217.25   $217.30  
  Purchase #3 $237.48   9.753%   $260.6414   $260.64   $260.65   $260.60  
  Purchase #4 $231.35   7.687%   $249.1339   $249.13   $249.15   $249.10  
  Purchase #5 $165.62   10.752%   $183.4275   $183.43   $183.45   $183.40  
  Purchase #6 $166.28   11.339%   $185.1345   $185.13   $185.15   $185.10  
  Purchase #7 $231.88   4.805%   $243.0218   $243.02   $243.00   $243.00  
  7 purchase totals = $1,402.11       $1,537.1235   $1,537.11   $1,537.15   $1,537.00