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	$246.90	6.319%	$262.5016	$262.50	$262.50	$262.50
Purchase #2	$137.99	10.820%	$152.9205	$152.92	$152.90	$152.90
Purchase #3	$235.60	4.194%	$245.4811	$245.48	$245.50	$245.50
Purchase #4	$18.65	8.718%	$20.2759	$20.28	$20.30	$20.30
Purchase #5	$229.28	13.283%	$259.7353	$259.74	$259.75	$259.70
Purchase #6	$49.92	11.178%	$55.5001	$55.50	$55.50	$55.50
Purchase #7	$131.95	4.374%	$137.7215	$137.72	$137.70	$137.70
7 purchase totals =	$1,050.29		$1,134.1360	$1,134.14	$1,134.15	$1,134.10