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 $189.63   8.359%   $205.4812   $205.48   $205.50   $205.50  
  Purchase #2 $137.55   7.237%   $147.5045   $147.50   $147.50   $147.50  
  Purchase #3 $46.88   5.760%   $49.5803   $49.58   $49.60   $49.60  
  Purchase #4 $99.70   7.453%   $107.1306   $107.13   $107.15   $107.10  
  Purchase #5 $175.79   11.449%   $195.9162   $195.92   $195.90   $195.90  
  Purchase #6 $246.31   13.515%   $279.5988   $279.60   $279.60   $279.60  
  Purchase #7 $231.76   10.587%   $256.2964   $256.30   $256.30   $256.30  
  7 purchase totals = $1,127.62       $1,241.5080   $1,241.51   $1,241.55   $1,241.50