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	$32.27	11.203%	$35.8852	$35.89	$35.90	$35.90
Purchase #2	$116.56	12.713%	$131.3783	$131.38	$131.40	$131.40
Purchase #3	$154.93	7.115%	$165.9533	$165.95	$165.95	$166.00
Purchase #4	$244.72	12.736%	$275.8875	$275.89	$275.90	$275.90
Purchase #5	$10.99	12.415%	$12.3544	$12.35	$12.35	$12.40
Purchase #6	$82.84	6.435%	$88.1708	$88.17	$88.15	$88.20
Purchase #7	$75.25	3.245%	$77.6919	$77.69	$77.70	$77.70
7 purchase totals =	$717.56		$787.3214	$787.32	$787.35	$787.50