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 $66.48   13.106%   $75.1929   $75.19   $75.20   $75.20  
  Purchase #2 $163.83   11.287%   $182.3215   $182.32   $182.30   $182.30  
  Purchase #3 $155.95   11.114%   $173.2823   $173.28   $173.30   $173.30  
  Purchase #4 $53.51   6.648%   $57.0673   $57.07   $57.05   $57.10  
  Purchase #5 $162.73   6.757%   $173.7257   $173.73   $173.75   $173.70  
  Purchase #6 $217.55   9.657%   $238.5588   $238.56   $238.55   $238.60  
  Purchase #7 $201.47   6.422%   $214.4084   $214.41   $214.40   $214.40  
  7 purchase totals = $1,021.52       $1,114.5569   $1,114.56   $1,114.55   $1,114.60