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	$137.80	12.844%	$155.499	$155.50	$155.50	$155.50
Purchase #2	$57.26	12.375%	$64.3459	$64.35	$64.35	$64.30
Purchase #3	$34.76	11.255%	$38.6722	$38.67	$38.65	$38.70
Purchase #4	$184.54	5.837%	$195.3116	$195.31	$195.30	$195.30
Purchase #5	$152.32	10.600%	$168.4659	$168.47	$168.45	$168.50
Purchase #6	$50.32	9.123%	$54.9107	$54.91	$54.90	$54.90
Purchase #7	$10.56	7.620%	$11.3647	$11.36	$11.35	$11.40
7 purchase totals =	$627.56		$688.5700	$688.57	$688.50	$688.60