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	$83.42	7.159%	$89.392	$89.39	$89.40	$89.40
Purchase #2	$235.59	4.166%	$245.4047	$245.40	$245.40	$245.40
Purchase #3	$134.35	5.103%	$141.2059	$141.21	$141.20	$141.20
Purchase #4	$155.46	9.512%	$170.2474	$170.25	$170.25	$170.20
Purchase #5	$227.49	5.313%	$239.5765	$239.58	$239.60	$239.60
Purchase #6	$87.63	13.125%	$99.1314	$99.13	$99.15	$99.10
Purchase #7	$88.48	3.128%	$91.2477	$91.25	$91.25	$91.20
7 purchase totals =	$1,012.42		$1,076.2056	$1,076.21	$1,076.25	$1,076.10