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	$55.76	9.186%	$60.8821	$60.88	$60.90	$60.90
Purchase #2	$33.75	6.170%	$35.8324	$35.83	$35.85	$35.80
Purchase #3	$54.61	9.508%	$59.8023	$59.80	$59.80	$59.80
Purchase #4	$135.76	11.405%	$151.2434	$151.24	$151.25	$151.20
Purchase #5	$17.25	6.845%	$18.4308	$18.43	$18.45	$18.40
Purchase #6	$39.50	3.561%	$40.9066	$40.91	$40.90	$40.90
Purchase #7	$236.57	5.106%	$248.6493	$248.65	$248.65	$248.60
7 purchase totals =	$573.20		$615.7469	$615.74	$615.80	$615.60