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 $114.66   9.663%   $125.7396   $125.74   $125.75   $125.70  
  Purchase #2 $222.67   10.843%   $246.8141   $246.81   $246.80   $246.80  
  Purchase #3 $139.81   5.404%   $147.3653   $147.37   $147.35   $147.40  
  Purchase #4 $25.63   7.700%   $27.6035   $27.60   $27.60   $27.60  
  Purchase #5 $62.40   10.673%   $69.06   $69.06   $69.05   $69.10  
  Purchase #6 $140.46   8.859%   $152.9034   $152.90   $152.90   $152.90  
  Purchase #7 $118.75   12.729%   $133.8657   $133.87   $133.85   $133.90  
  7 purchase totals = $824.38       $903.3516   $903.35   $903.30   $903.40