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	$152.90	11.238%	$170.0829	$170.08	$170.10	$170.10
Purchase #2	$91.72	6.227%	$97.4314	$97.43	$97.45	$97.40
Purchase #3	$102.64	10.211%	$113.1206	$113.12	$113.10	$113.10
Purchase #4	$35.32	7.311%	$37.9022	$37.90	$37.90	$37.90
Purchase #5	$12.58	10.785%	$13.9368	$13.94	$13.95	$13.90
Purchase #6	$173.73	13.287%	$196.8135	$196.81	$196.80	$196.80
Purchase #7	$51.46	6.408%	$54.7576	$54.76	$54.75	$54.80
7 purchase totals =	$620.35		$684.0450	$684.04	$684.05	$684.00