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	$50.72	7.261%	$54.4028	$54.40	$54.40	$54.40
Purchase #2	$183.66	13.293%	$208.0739	$208.07	$208.05	$208.10
Purchase #3	$167.94	10.704%	$185.9163	$185.92	$185.90	$185.90
Purchase #4	$228.55	6.151%	$242.6081	$242.61	$242.60	$242.60
Purchase #5	$89.82	12.635%	$101.1688	$101.17	$101.15	$101.20
Purchase #6	$64.75	11.851%	$72.4235	$72.42	$72.40	$72.40
Purchase #7	$32.31	4.203%	$33.668	$33.67	$33.65	$33.70
7 purchase totals =	$817.75		$898.2614	$898.26	$898.15	$898.30