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	$151.43	3.578%	$156.8482	$156.85	$156.85	$156.80
Purchase #2	$92.26	13.178%	$104.418	$104.42	$104.40	$104.40
Purchase #3	$98.58	7.206%	$105.6837	$105.68	$105.70	$105.70
Purchase #4	$246.57	13.535%	$279.9432	$279.94	$279.95	$279.90
Purchase #5	$38.64	10.442%	$42.6748	$42.67	$42.65	$42.70
Purchase #6	$232.90	9.451%	$254.9114	$254.91	$254.90	$254.90
Purchase #7	$121.25	12.185%	$136.0243	$136.02	$136.00	$136.00
7 purchase totals =	$981.63		$1,080.5036	$1,080.49	$1,080.45	$1,080.40