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 $241.66   8.492%   $262.1818   $262.18   $262.20   $262.20  
  Purchase #2 $21.82   10.118%   $24.0277   $24.03   $24.05   $24.00  
  Purchase #3 $199.59   10.471%   $220.4891   $220.49   $220.50   $220.50  
  Purchase #4 $196.92   7.189%   $211.0766   $211.08   $211.10   $211.10  
  Purchase #5 $177.29   3.556%   $183.5944   $183.59   $183.60   $183.60  
  Purchase #6 $98.73   6.104%   $104.7565   $104.76   $104.75   $104.80  
  Purchase #7 $249.95   10.842%   $277.0496   $277.05   $277.05   $277.00  
  7 purchase totals = $1,185.96       $1,283.1757   $1,283.18   $1,283.25   $1,283.20