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	$78.28	13.739%	$89.0349	$89.03	$89.05	$89.00
Purchase #2	$221.45	5.375%	$233.3529	$233.35	$233.35	$233.40
Purchase #3	$249.50	13.249%	$282.5563	$282.56	$282.55	$282.60
Purchase #4	$9.41	13.370%	$10.6681	$10.67	$10.65	$10.70
Purchase #5	$99.96	5.445%	$105.4028	$105.40	$105.40	$105.40
Purchase #6	$209.99	10.426%	$231.8836	$231.88	$231.90	$231.90
Purchase #7	$26.76	13.299%	$30.3188	$30.32	$30.30	$30.30
7 purchase totals =	$895.35		$983.2174	$983.21	$983.20	$983.30