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 $246.26   3.597%   $255.118   $255.12   $255.10   $255.10  
  Purchase #2 $11.48   4.197%   $11.9618   $11.96   $11.95   $12.00  
  Purchase #3 $52.98   9.716%   $58.1275   $58.13   $58.15   $58.10  
  Purchase #4 $8.91   5.592%   $9.4082   $9.41   $9.40   $9.40  
  Purchase #5 $187.44   5.556%   $197.8542   $197.85   $197.85   $197.90  
  Purchase #6 $245.38   6.209%   $260.6156   $260.62   $260.60   $260.60  
  Purchase #7 $146.84   3.147%   $151.4611   $151.46   $151.45   $151.50  
  7 purchase totals = $899.29       $944.5464   $944.55   $944.50   $944.60