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	$146.89	6.314%	$156.1646	$156.16	$156.15	$156.20
Purchase #2	$79.39	12.267%	$89.1288	$89.13	$89.15	$89.10
Purchase #3	$117.36	9.348%	$128.3308	$128.33	$128.35	$128.30
Purchase #4	$210.89	10.465%	$232.9596	$232.96	$232.95	$233.00
Purchase #5	$108.69	12.484%	$122.2589	$122.26	$122.25	$122.30
Purchase #6	$102.67	11.618%	$114.5982	$114.60	$114.60	$114.60
Purchase #7	$130.85	5.160%	$137.6019	$137.60	$137.60	$137.60
7 purchase totals =	$896.74		$981.0428	$981.04	$981.05	$981.10