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 $246.46   5.723%   $260.5649   $260.56   $260.55   $260.60  
  Purchase #2 $58.67   8.710%   $63.7802   $63.78   $63.80   $63.80  
  Purchase #3 $84.76   11.763%   $94.7303   $94.73   $94.75   $94.70  
  Purchase #4 $118.84   3.177%   $122.6155   $122.62   $122.60   $122.60  
  Purchase #5 $241.69   8.700%   $262.717   $262.72   $262.70   $262.70  
  Purchase #6 $137.28   4.554%   $143.5317   $143.53   $143.55   $143.50  
  Purchase #7 $67.55   11.251%   $75.1501   $75.15   $75.15   $75.20  
  7 purchase totals = $955.25       $1,023.0897   $1,023.09   $1,023.10   $1,023.10