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	$17.83	12.507%	$20.06	$20.06	$20.05	$20.10
Purchase #2	$71.87	9.128%	$78.4303	$78.43	$78.45	$78.40
Purchase #3	$207.52	7.644%	$223.3828	$223.38	$223.40	$223.40
Purchase #4	$121.44	7.774%	$130.8807	$130.88	$130.90	$130.90
Purchase #5	$248.87	6.554%	$265.1809	$265.18	$265.20	$265.20
Purchase #6	$133.40	4.206%	$139.0108	$139.01	$139.00	$139.00
Purchase #7	$34.26	8.692%	$37.2379	$37.24	$37.25	$37.20
7 purchase totals =	$835.19		$894.1834	$894.18	$894.25	$894.20