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 $30.70   6.608%   $32.7287   $32.73   $32.75   $32.70  
  Purchase #2 $175.91   3.143%   $181.4389   $181.44   $181.45   $181.40  
  Purchase #3 $114.65   3.443%   $118.5974   $118.60   $118.60   $118.60  
  Purchase #4 $179.41   8.646%   $194.9218   $194.92   $194.90   $194.90  
  Purchase #5 $173.95   4.437%   $181.6682   $181.67   $181.65   $181.70  
  Purchase #6 $48.42   5.269%   $50.9712   $50.97   $50.95   $51.00  
  Purchase #7 $119.27   5.613%   $125.9646   $125.96   $125.95   $126.00  
  7 purchase totals = $842.31       $886.2908   $886.29   $886.25   $886.30