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	$64.31	9.388%	$70.3474	$70.35	$70.35	$70.30
Purchase #2	$155.83	7.625%	$167.712	$167.71	$167.70	$167.70
Purchase #3	$54.25	6.662%	$57.8641	$57.86	$57.85	$57.90
Purchase #4	$140.44	3.171%	$144.8934	$144.89	$144.90	$144.90
Purchase #5	$105.46	12.665%	$118.8165	$118.82	$118.80	$118.80
Purchase #6	$217.32	13.741%	$247.1819	$247.18	$247.20	$247.20
Purchase #7	$39.98	13.697%	$45.4561	$45.46	$45.45	$45.50
7 purchase totals =	$777.59		$852.2714	$852.27	$852.25	$852.30