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 $58.88   3.463%   $60.919   $60.92   $60.90   $60.90  
  Purchase #2 $19.26   6.864%   $20.582   $20.58   $20.60   $20.60  
  Purchase #3 $49.38   10.360%   $54.4958   $54.50   $54.50   $54.50  
  Purchase #4 $55.82   11.491%   $62.2343   $62.23   $62.25   $62.20  
  Purchase #5 $106.26   5.506%   $112.1107   $112.11   $112.10   $112.10  
  Purchase #6 $203.83   10.330%   $224.8856   $224.89   $224.90   $224.90  
  Purchase #7 $58.70   5.545%   $61.9549   $61.95   $61.95   $62.00  
  7 purchase totals = $552.13       $597.1823   $597.18   $597.20   $597.20