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	$97.58	11.574%	$108.8739	$108.87	$108.85	$108.90
Purchase #2	$174.31	8.834%	$189.7085	$189.71	$189.70	$189.70
Purchase #3	$205.32	11.700%	$229.3424	$229.34	$229.35	$229.30
Purchase #4	$120.62	5.502%	$127.2565	$127.26	$127.25	$127.30
Purchase #5	$168.56	5.866%	$178.4477	$178.45	$178.45	$178.40
Purchase #6	$29.38	10.373%	$32.4276	$32.43	$32.45	$32.40
Purchase #7	$78.77	11.842%	$88.0979	$88.10	$88.10	$88.10
7 purchase totals =	$874.54		$954.1545	$954.16	$954.15	$954.10