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 $63.31   5.160%   $66.5768   $66.58   $66.60   $66.60  
  Purchase #2 $159.43   13.203%   $180.4795   $180.48   $180.50   $180.50  
  Purchase #3 $118.78   13.309%   $134.5884   $134.59   $134.60   $134.60  
  Purchase #4 $234.49   5.553%   $247.5112   $247.51   $247.50   $247.50  
  Purchase #5 $245.58   8.289%   $265.9361   $265.94   $265.95   $265.90  
  Purchase #6 $143.83   11.589%   $160.4985   $160.50   $160.50   $160.50  
  Purchase #7 $201.33   6.669%   $214.7567   $214.76   $214.75   $214.80  
  7 purchase totals = $1,166.75       $1,270.3472   $1,270.36   $1,270.40   $1,270.40