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	$59.33	11.323%	$66.0479	$66.05	$66.05	$66.00
Purchase #2	$29.33	9.562%	$32.1345	$32.13	$32.15	$32.10
Purchase #3	$35.45	9.689%	$38.8848	$38.88	$38.90	$38.90
Purchase #4	$14.41	5.777%	$15.2425	$15.24	$15.25	$15.20
Purchase #5	$140.88	10.388%	$155.5146	$155.51	$155.50	$155.50
Purchase #6	$231.69	6.121%	$245.8717	$245.87	$245.85	$245.90
Purchase #7	$89.66	5.393%	$94.4954	$94.50	$94.50	$94.50
7 purchase totals =	$600.75		$648.1914	$648.18	$648.20	$648.10