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 $211.41   12.467%   $237.7665   $237.77   $237.75   $237.80  
  Purchase #2 $148.95   4.548%   $155.7242   $155.72   $155.70   $155.70  
  Purchase #3 $227.53   12.231%   $255.3592   $255.36   $255.35   $255.40  
  Purchase #4 $163.87   12.372%   $184.144   $184.14   $184.15   $184.10  
  Purchase #5 $84.61   7.487%   $90.9448   $90.94   $90.95   $90.90  
  Purchase #6 $94.46   3.664%   $97.921   $97.92   $97.90   $97.90  
  Purchase #7 $219.81   7.521%   $236.3419   $236.34   $236.35   $236.30  
  7 purchase totals = $1,150.64       $1,258.2016   $1,258.19   $1,258.15   $1,258.10