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	$24.76	9.769%	$27.1788	$27.18	$27.20	$27.20
Purchase #2	$77.56	4.191%	$80.8105	$80.81	$80.80	$80.80
Purchase #3	$82.93	11.171%	$92.1941	$92.19	$92.20	$92.20
Purchase #4	$242.44	4.423%	$253.1631	$253.16	$253.15	$253.20
Purchase #5	$210.40	5.544%	$222.0646	$222.06	$222.05	$222.10
Purchase #6	$148.86	6.675%	$158.7964	$158.80	$158.80	$158.80
Purchase #7	$219.51	5.600%	$231.8026	$231.80	$231.80	$231.80
7 purchase totals =	$1,006.46		$1,066.0101	$1,066.00	$1,066.00	$1,066.10