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	$26.27	8.188%	$28.421	$28.42	$28.40	$28.40
Purchase #2	$40.60	10.680%	$44.9361	$44.94	$44.95	$44.90
Purchase #3	$176.88	4.659%	$185.1208	$185.12	$185.10	$185.10
Purchase #4	$80.99	10.429%	$89.4364	$89.44	$89.45	$89.40
Purchase #5	$243.37	9.369%	$266.1713	$266.17	$266.15	$266.20
Purchase #6	$233.92	3.266%	$241.5598	$241.56	$241.55	$241.60
Purchase #7	$122.73	12.319%	$137.8491	$137.85	$137.85	$137.80
7 purchase totals =	$924.76		$993.4945	$993.50	$993.45	$993.40