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 $6.46   8.490%   $7.0085   $7.01   $7.00   $7.00  
  Purchase #2 $217.73   8.822%   $236.9381   $236.94   $236.95   $236.90  
  Purchase #3 $17.85   3.138%   $18.4101   $18.41   $18.40   $18.40  
  Purchase #4 $248.89   5.391%   $262.3077   $262.31   $262.30   $262.30  
  Purchase #5 $162.98   9.132%   $177.8633   $177.86   $177.85   $177.90  
  Purchase #6 $133.39   12.378%   $149.901   $149.90   $149.90   $149.90  
  Purchase #7 $144.55   12.144%   $162.1042   $162.10   $162.10   $162.10  
  7 purchase totals = $931.85       $1,014.5329   $1,014.53   $1,014.50   $1,014.50