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	$119.34	6.827%	$127.4873	$127.49	$127.50	$127.50
Purchase #2	$50.30	9.784%	$55.2214	$55.22	$55.20	$55.20
Purchase #3	$19.58	6.758%	$20.9032	$20.90	$20.90	$20.90
Purchase #4	$190.75	5.234%	$200.7339	$200.73	$200.75	$200.70
Purchase #5	$130.75	7.616%	$140.7079	$140.71	$140.70	$140.70
Purchase #6	$226.29	11.444%	$252.1866	$252.19	$252.20	$252.20
Purchase #7	$31.51	5.306%	$33.1819	$33.18	$33.20	$33.20
7 purchase totals =	$768.52		$830.4222	$830.42	$830.45	$830.40