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 $160.88   13.733%   $182.9737   $182.97   $182.95   $183.00  
  Purchase #2 $54.29   4.237%   $56.5903   $56.59   $56.60   $56.60  
  Purchase #3 $225.35   8.558%   $244.6355   $244.64   $244.65   $244.60  
  Purchase #4 $176.54   3.111%   $182.0322   $182.03   $182.05   $182.00  
  Purchase #5 $125.88   5.456%   $132.748   $132.75   $132.75   $132.70  
  Purchase #6 $208.27   7.249%   $223.3675   $223.37   $223.35   $223.40  
  Purchase #7 $187.93   13.546%   $213.387   $213.39   $213.40   $213.40  
  7 purchase totals = $1,139.14       $1,235.7342   $1,235.74   $1,235.75   $1,235.70