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 $231.61   10.374%   $255.6372   $255.64   $255.65   $255.60  
  Purchase #2 $116.59   6.807%   $124.5263   $124.53   $124.55   $124.50  
  Purchase #3 $175.95   3.871%   $182.761   $182.76   $182.75   $182.80  
  Purchase #4 $246.41   13.500%   $279.6754   $279.68   $279.70   $279.70  
  Purchase #5 $106.78   6.755%   $113.993   $113.99   $114.00   $114.00  
  Purchase #6 $60.37   5.680%   $63.799   $63.80   $63.80   $63.80  
  Purchase #7 $99.87   10.817%   $110.6729   $110.67   $110.65   $110.70  
  7 purchase totals = $1,037.58       $1,131.0648   $1,131.07   $1,131.10   $1,131.10