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	$80.75	11.470%	$90.012	$90.01	$90.00	$90.00
Purchase #2	$132.79	10.116%	$146.223	$146.22	$146.20	$146.20
Purchase #3	$22.67	13.389%	$25.7053	$25.71	$25.70	$25.70
Purchase #4	$104.42	13.670%	$118.6942	$118.69	$118.70	$118.70
Purchase #5	$219.79	4.209%	$229.041	$229.04	$229.05	$229.00
Purchase #6	$96.97	12.580%	$109.1688	$109.17	$109.15	$109.20
Purchase #7	$30.39	12.837%	$34.2912	$34.29	$34.30	$34.30
7 purchase totals =	$687.78		$753.1355	$753.13	$753.10	$753.10