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	$67.60	10.546%	$74.7291	$74.73	$74.75	$74.70
Purchase #2	$57.69	13.200%	$65.3051	$65.31	$65.30	$65.30
Purchase #3	$223.72	3.219%	$230.9215	$230.92	$230.90	$230.90
Purchase #4	$32.74	8.386%	$35.4856	$35.49	$35.50	$35.50
Purchase #5	$35.42	4.696%	$37.0833	$37.08	$37.10	$37.10
Purchase #6	$100.33	5.186%	$105.5331	$105.53	$105.55	$105.50
Purchase #7	$8.44	4.489%	$8.8189	$8.82	$8.80	$8.80
7 purchase totals =	$525.94		$557.8766	$557.88	$557.90	$557.80