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	$18.90	6.157%	$20.0637	$20.06	$20.05	$20.10
Purchase #2	$162.81	5.336%	$171.4975	$171.50	$171.50	$171.50
Purchase #3	$18.33	3.246%	$18.925	$18.93	$18.95	$18.90
Purchase #4	$106.51	3.567%	$110.3092	$110.31	$110.30	$110.30
Purchase #5	$79.79	7.304%	$85.6179	$85.62	$85.60	$85.60
Purchase #6	$59.36	11.418%	$66.1377	$66.14	$66.15	$66.10
Purchase #7	$11.55	10.150%	$12.7223	$12.72	$12.70	$12.70
7 purchase totals =	$457.25		$485.2733	$485.28	$485.25	$485.20