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 $92.72   5.782%   $98.0811   $98.08   $98.10   $98.10  
  Purchase #2 $74.35   5.817%   $78.6749   $78.67   $78.65   $78.70  
  Purchase #3 $161.28   7.729%   $173.7453   $173.75   $173.75   $173.70  
  Purchase #4 $233.61   9.199%   $255.0998   $255.10   $255.10   $255.10  
  Purchase #5 $161.92   13.316%   $183.4813   $183.48   $183.50   $183.50  
  Purchase #6 $140.88   9.455%   $154.2002   $154.20   $154.20   $154.20  
  Purchase #7 $237.51   9.303%   $259.6056   $259.61   $259.60   $259.60  
  7 purchase totals = $1,102.27       $1,202.8882   $1,202.89   $1,202.90   $1,202.90