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 $236.62   13.363%   $268.2395   $268.24   $268.25   $268.20  
  Purchase #2 $204.34   6.262%   $217.1358   $217.14   $217.15   $217.10  
  Purchase #3 $49.66   7.354%   $53.312   $53.31   $53.30   $53.30  
  Purchase #4 $231.56   4.830%   $242.7443   $242.74   $242.75   $242.70  
  Purchase #5 $126.28   3.475%   $130.6682   $130.67   $130.65   $130.70  
  Purchase #6 $62.48   13.117%   $70.6755   $70.68   $70.70   $70.70  
  Purchase #7 $223.95   3.248%   $231.2239   $231.22   $231.20   $231.20  
  7 purchase totals = $1,134.89       $1,213.9992   $1,214.00   $1,214.00   $1,213.90