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	$33.89	4.187%	$35.309	$35.31	$35.30	$35.30
Purchase #2	$104.67	13.547%	$118.8496	$118.85	$118.85	$118.80
Purchase #3	$143.30	7.399%	$153.9028	$153.90	$153.90	$153.90
Purchase #4	$6.57	8.511%	$7.1292	$7.13	$7.15	$7.10
Purchase #5	$13.81	11.129%	$15.3469	$15.35	$15.35	$15.30
Purchase #6	$110.78	4.557%	$115.8282	$115.83	$115.85	$115.80
Purchase #7	$79.89	11.275%	$88.8976	$88.90	$88.90	$88.90
7 purchase totals =	$492.91		$535.2633	$535.27	$535.30	$535.10