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	$238.74	10.672%	$264.2183	$264.22	$264.20	$264.20
Purchase #2	$28.81	12.388%	$32.379	$32.38	$32.40	$32.40
Purchase #3	$47.59	3.403%	$49.2095	$49.21	$49.20	$49.20
Purchase #4	$64.59	3.585%	$66.9056	$66.91	$66.90	$66.90
Purchase #5	$65.39	7.861%	$70.5303	$70.53	$70.55	$70.50
Purchase #6	$242.38	9.465%	$265.3213	$265.32	$265.30	$265.30
Purchase #7	$116.65	10.350%	$128.7233	$128.72	$128.70	$128.70
7 purchase totals =	$804.15		$877.2873	$877.29	$877.25	$877.20