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	$106.53	4.482%	$111.3047	$111.30	$111.30	$111.30
Purchase #2	$60.98	8.321%	$66.0541	$66.05	$66.05	$66.10
Purchase #3	$153.35	8.813%	$166.8647	$166.86	$166.85	$166.90
Purchase #4	$216.76	12.107%	$243.0031	$243.00	$243.00	$243.00
Purchase #5	$92.92	13.314%	$105.2914	$105.29	$105.30	$105.30
Purchase #6	$143.85	9.138%	$156.995	$157.00	$157.00	$157.00
Purchase #7	$162.78	4.778%	$170.5576	$170.56	$170.55	$170.60
7 purchase totals =	$937.17		$1,020.0706	$1,020.06	$1,020.05	$1,020.20