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	$7.69	6.301%	$8.1745	$8.17	$8.15	$8.20
Purchase #2	$39.51	9.235%	$43.1587	$43.16	$43.15	$43.20
Purchase #3	$20.50	5.530%	$21.6337	$21.63	$21.65	$21.60
Purchase #4	$28.95	10.636%	$32.0291	$32.03	$32.05	$32.00
Purchase #5	$203.84	6.199%	$216.476	$216.48	$216.50	$216.50
Purchase #6	$28.75	8.756%	$31.2674	$31.27	$31.25	$31.30
Purchase #7	$86.26	5.634%	$91.1199	$91.12	$91.10	$91.10
7 purchase totals =	$415.50		$443.8593	$443.86	$443.85	$443.90