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	$129.58	3.109%	$133.6086	$133.61	$133.60	$133.60
Purchase #2	$247.33	9.825%	$271.6302	$271.63	$271.65	$271.60
Purchase #3	$205.73	8.817%	$223.8692	$223.87	$223.85	$223.90
Purchase #4	$29.47	13.782%	$33.5316	$33.53	$33.55	$33.50
Purchase #5	$16.33	12.655%	$18.3966	$18.40	$18.40	$18.40
Purchase #6	$37.80	11.470%	$42.1357	$42.14	$42.15	$42.10
Purchase #7	$12.51	6.434%	$13.3149	$13.31	$13.30	$13.30
7 purchase totals =	$678.75		$736.4868	$736.49	$736.50	$736.40