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	$239.47	4.501%	$250.2485	$250.25	$250.25	$250.20
Purchase #2	$159.89	13.469%	$181.4256	$181.43	$181.45	$181.40
Purchase #3	$53.27	11.689%	$59.4967	$59.50	$59.50	$59.50
Purchase #4	$217.62	9.805%	$238.9576	$238.96	$238.95	$239.00
Purchase #5	$11.26	3.641%	$11.67	$11.67	$11.65	$11.70
Purchase #6	$96.89	8.831%	$105.4464	$105.45	$105.45	$105.40
Purchase #7	$26.57	3.132%	$27.4022	$27.40	$27.40	$27.40
7 purchase totals =	$804.97		$874.6470	$874.66	$874.65	$874.60