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	$25.33	10.618%	$28.0195	$28.02	$28.00	$28.00
Purchase #2	$106.86	11.796%	$119.4652	$119.47	$119.45	$119.50
Purchase #3	$35.73	4.420%	$37.3093	$37.31	$37.30	$37.30
Purchase #4	$224.37	6.218%	$238.3213	$238.32	$238.30	$238.30
Purchase #5	$76.32	7.700%	$82.1966	$82.20	$82.20	$82.20
Purchase #6	$99.75	8.624%	$108.3524	$108.35	$108.35	$108.40
Purchase #7	$225.39	3.413%	$233.0826	$233.08	$233.10	$233.10
7 purchase totals =	$793.75		$846.7469	$846.75	$846.70	$846.80