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	$32.38	10.510%	$35.7831	$35.78	$35.80	$35.80
Purchase #2	$203.75	8.229%	$220.5166	$220.52	$220.50	$220.50
Purchase #3	$35.25	4.717%	$36.9127	$36.91	$36.90	$36.90
Purchase #4	$248.31	6.251%	$263.8319	$263.83	$263.85	$263.80
Purchase #5	$118.73	13.416%	$134.6588	$134.66	$134.65	$134.70
Purchase #6	$189.83	3.402%	$196.288	$196.29	$196.30	$196.30
Purchase #7	$90.27	4.255%	$94.111	$94.11	$94.10	$94.10
7 purchase totals =	$918.52		$982.1021	$982.10	$982.10	$982.10