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	$110.77	9.436%	$121.2223	$121.22	$121.20	$121.20
Purchase #2	$59.60	13.111%	$67.4142	$67.41	$67.40	$67.40
Purchase #3	$131.76	8.161%	$142.5129	$142.51	$142.50	$142.50
Purchase #4	$55.76	3.810%	$57.8845	$57.88	$57.90	$57.90
Purchase #5	$242.25	13.725%	$275.4988	$275.50	$275.50	$275.50
Purchase #6	$40.52	11.862%	$45.3265	$45.33	$45.35	$45.30
Purchase #7	$22.55	4.653%	$23.5993	$23.60	$23.60	$23.60
7 purchase totals =	$663.21		$733.4585	$733.45	$733.45	$733.40