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	$34.63	13.542%	$39.3196	$39.32	$39.30	$39.30
Purchase #2	$136.91	8.576%	$148.6514	$148.65	$148.65	$148.70
Purchase #3	$52.87	5.709%	$55.8883	$55.89	$55.90	$55.90
Purchase #4	$169.53	13.226%	$191.952	$191.95	$191.95	$192.00
Purchase #5	$131.72	6.130%	$139.7944	$139.79	$139.80	$139.80
Purchase #6	$196.32	11.706%	$219.3012	$219.30	$219.30	$219.30
Purchase #7	$224.74	5.712%	$237.5771	$237.58	$237.60	$237.60
7 purchase totals =	$946.72		$1,032.4840	$1,032.48	$1,032.50	$1,032.60