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	$127.62	11.188%	$141.8981	$141.90	$141.90	$141.90
Purchase #2	$185.87	11.438%	$207.1298	$207.13	$207.15	$207.10
Purchase #3	$140.40	13.236%	$158.9833	$158.98	$159.00	$159.00
Purchase #4	$89.82	6.283%	$95.4634	$95.46	$95.45	$95.50
Purchase #5	$209.69	3.167%	$216.3309	$216.33	$216.35	$216.30
Purchase #6	$136.39	5.415%	$143.7755	$143.78	$143.80	$143.80
Purchase #7	$112.71	3.325%	$116.4576	$116.46	$116.45	$116.50
7 purchase totals =	$1,002.50		$1,080.0386	$1,080.04	$1,080.10	$1,080.10