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	$137.30	13.117%	$155.3096	$155.31	$155.30	$155.30
Purchase #2	$184.64	8.275%	$199.919	$199.92	$199.90	$199.90
Purchase #3	$73.75	13.734%	$83.8788	$83.88	$83.90	$83.90
Purchase #4	$157.26	9.625%	$172.3963	$172.40	$172.40	$172.40
Purchase #5	$69.78	9.511%	$76.4168	$76.42	$76.40	$76.40
Purchase #6	$244.78	12.337%	$274.9785	$274.98	$275.00	$275.00
Purchase #7	$83.69	6.205%	$88.883	$88.88	$88.90	$88.90
7 purchase totals =	$951.20		$1,051.7820	$1,051.79	$1,051.80	$1,051.80