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 $238.98   6.430%   $254.3464   $254.35   $254.35   $254.30  
  Purchase #2 $146.56   8.659%   $159.2506   $159.25   $159.25   $159.30  
  Purchase #3 $187.91   6.606%   $200.3233   $200.32   $200.30   $200.30  
  Purchase #4 $18.62   5.247%   $19.597   $19.60   $19.60   $19.60  
  Purchase #5 $159.50   8.662%   $173.3159   $173.32   $173.30   $173.30  
  Purchase #6 $238.54   13.811%   $271.4848   $271.48   $271.50   $271.50  
  Purchase #7 $25.55   3.419%   $26.4236   $26.42   $26.40   $26.40  
  7 purchase totals = $1,015.66       $1,104.7416   $1,104.74   $1,104.70   $1,104.70