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	$22.72	8.713%	$24.6996	$24.70	$24.70	$24.70
Purchase #2	$99.43	10.323%	$109.6942	$109.69	$109.70	$109.70
Purchase #3	$218.45	5.123%	$229.6412	$229.64	$229.65	$229.60
Purchase #4	$82.41	8.808%	$89.6687	$89.67	$89.65	$89.70
Purchase #5	$197.38	11.390%	$219.8616	$219.86	$219.85	$219.90
Purchase #6	$189.65	10.371%	$209.3186	$209.32	$209.30	$209.30
Purchase #7	$231.94	4.180%	$241.6351	$241.64	$241.65	$241.60
7 purchase totals =	$1,041.98		$1,124.5190	$1,124.52	$1,124.50	$1,124.50