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 $52.75   12.206%   $59.1887   $59.19   $59.20   $59.20  
  Purchase #2 $210.96   9.194%   $230.3557   $230.36   $230.35   $230.40  
  Purchase #3 $78.41   11.240%   $87.2233   $87.22   $87.20   $87.20  
  Purchase #4 $248.96   4.841%   $261.0122   $261.01   $261.00   $261.00  
  Purchase #5 $198.34   9.173%   $216.5337   $216.53   $216.55   $216.50  
  Purchase #6 $227.38   12.318%   $255.3887   $255.39   $255.40   $255.40  
  Purchase #7 $185.85   13.494%   $210.9286   $210.93   $210.95   $210.90  
  7 purchase totals = $1,202.65       $1,320.6309   $1,320.63   $1,320.65   $1,320.60