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 $232.80   10.643%   $257.5769   $257.58   $257.60   $257.60  
  Purchase #2 $209.86   3.553%   $217.3163   $217.32   $217.30   $217.30  
  Purchase #3 $220.53   7.111%   $236.2119   $236.21   $236.20   $236.20  
  Purchase #4 $75.36   12.240%   $84.5841   $84.58   $84.60   $84.60  
  Purchase #5 $91.39   4.651%   $95.6405   $95.64   $95.65   $95.60  
  Purchase #6 $71.58   11.286%   $79.6585   $79.66   $79.65   $79.70  
  Purchase #7 $247.47   9.213%   $270.2694   $270.27   $270.25   $270.30  
  7 purchase totals = $1,148.99       $1,241.2576   $1,241.26   $1,241.25   $1,241.30