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 $154.43   12.414%   $173.6009   $173.60   $173.60   $173.60  
  Purchase #2 $237.62   6.670%   $253.4693   $253.47   $253.45   $253.50  
  Purchase #3 $121.49   11.542%   $135.5124   $135.51   $135.50   $135.50  
  Purchase #4 $169.84   7.303%   $182.2434   $182.24   $182.25   $182.20  
  Purchase #5 $226.55   6.767%   $241.8806   $241.88   $241.90   $241.90  
  Purchase #6 $110.48   13.453%   $125.3429   $125.34   $125.35   $125.30  
  Purchase #7 $22.49   13.716%   $25.5747   $25.57   $25.55   $25.60  
  7 purchase totals = $1,042.90       $1,137.6242   $1,137.61   $1,137.60   $1,137.60