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	$232.81	9.527%	$254.9898	$254.99	$255.00	$255.00
Purchase #2	$205.53	5.251%	$216.3224	$216.32	$216.30	$216.30
Purchase #3	$32.93	13.467%	$37.3647	$37.36	$37.35	$37.40
Purchase #4	$87.41	12.738%	$98.5443	$98.54	$98.55	$98.50
Purchase #5	$97.31	8.403%	$105.487	$105.49	$105.50	$105.50
Purchase #6	$59.27	13.230%	$67.1114	$67.11	$67.10	$67.10
Purchase #7	$112.88	13.739%	$128.3886	$128.39	$128.40	$128.40
7 purchase totals =	$828.14		$908.2082	$908.20	$908.20	$908.20