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	$11.93	4.787%	$12.5011	$12.50	$12.50	$12.50
Purchase #2	$185.72	6.621%	$198.0165	$198.02	$198.00	$198.00
Purchase #3	$133.53	9.713%	$146.4998	$146.50	$146.50	$146.50
Purchase #4	$202.26	13.389%	$229.3406	$229.34	$229.35	$229.30
Purchase #5	$34.54	9.294%	$37.7501	$37.75	$37.75	$37.80
Purchase #6	$20.29	6.808%	$21.6713	$21.67	$21.65	$21.70
Purchase #7	$79.72	7.458%	$85.6655	$85.67	$85.65	$85.70
7 purchase totals =	$667.99		$731.4449	$731.45	$731.40	$731.50