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 $180.94   12.704%   $203.9266   $203.93   $203.95   $203.90  
  Purchase #2 $117.54   12.750%   $132.5264   $132.53   $132.55   $132.50  
  Purchase #3 $30.64   7.510%   $32.9411   $32.94   $32.95   $32.90  
  Purchase #4 $235.86   13.778%   $268.3568   $268.36   $268.35   $268.40  
  Purchase #5 $73.88   3.649%   $76.5759   $76.58   $76.60   $76.60  
  Purchase #6 $39.99   4.874%   $41.9391   $41.94   $41.95   $41.90  
  Purchase #7 $125.64   3.149%   $129.5964   $129.60   $129.60   $129.60  
  7 purchase totals = $804.49       $885.8623   $885.88   $885.95   $885.80