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 $29.62   8.175%   $32.0414   $32.04   $32.05   $32.00  
  Purchase #2 $176.36   9.593%   $193.2782   $193.28   $193.30   $193.30  
  Purchase #3 $156.45   9.561%   $171.4082   $171.41   $171.40   $171.40  
  Purchase #4 $95.56   9.634%   $104.7663   $104.77   $104.75   $104.80  
  Purchase #5 $172.63   6.756%   $184.2929   $184.29   $184.30   $184.30  
  Purchase #6 $44.81   7.402%   $48.1268   $48.13   $48.15   $48.10  
  Purchase #7 $207.69   13.715%   $236.1747   $236.17   $236.15   $236.20  
  7 purchase totals = $883.12       $970.0885   $970.09   $970.10   $970.10