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 $82.93   11.419%   $92.3998   $92.40   $92.40   $92.40  
  Purchase #2 $146.97   3.236%   $151.7259   $151.73   $151.75   $151.70  
  Purchase #3 $146.75   9.779%   $161.1007   $161.10   $161.10   $161.10  
  Purchase #4 $249.56   3.235%   $257.6333   $257.63   $257.65   $257.60  
  Purchase #5 $223.63   12.485%   $251.5502   $251.55   $251.55   $251.60  
  Purchase #6 $93.75   9.538%   $102.6919   $102.69   $102.70   $102.70  
  Purchase #7 $209.78   6.388%   $223.1807   $223.18   $223.20   $223.20  
  7 purchase totals = $1,153.37       $1,240.2825   $1,240.28   $1,240.35   $1,240.30