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 $236.35   10.712%   $261.6678   $261.67   $261.65   $261.70  
  Purchase #2 $203.39   5.596%   $214.7717   $214.77   $214.75   $214.80  
  Purchase #3 $132.56   10.112%   $145.9645   $145.96   $145.95   $146.00  
  Purchase #4 $176.61   11.534%   $196.9802   $196.98   $197.00   $197.00  
  Purchase #5 $49.42   4.703%   $51.7442   $51.74   $51.75   $51.70  
  Purchase #6 $18.34   7.837%   $19.7773   $19.78   $19.80   $19.80  
  Purchase #7 $57.78   11.289%   $64.3028   $64.30   $64.30   $64.30  
  7 purchase totals = $874.45       $955.2085   $955.20   $955.20   $955.30