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 $243.75   13.668%   $277.0658   $277.07   $277.05   $277.10  
  Purchase #2 $236.61   8.564%   $256.8733   $256.87   $256.85   $256.90  
  Purchase #3 $169.42   4.516%   $177.071   $177.07   $177.05   $177.10  
  Purchase #4 $121.92   3.183%   $125.8007   $125.80   $125.80   $125.80  
  Purchase #5 $113.88   11.152%   $126.5799   $126.58   $126.60   $126.60  
  Purchase #6 $30.53   10.277%   $33.6676   $33.67   $33.65   $33.70  
  Purchase #7 $207.56   12.596%   $233.7043   $233.70   $233.70   $233.70  
  7 purchase totals = $1,123.67       $1,230.7626   $1,230.76   $1,230.70   $1,230.90