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	$42.38	7.132%	$45.4025	$45.40	$45.40	$45.40
Purchase #2	$234.68	3.191%	$242.1686	$242.17	$242.15	$242.20
Purchase #3	$68.31	6.242%	$72.5739	$72.57	$72.55	$72.60
Purchase #4	$248.89	5.390%	$262.3052	$262.31	$262.30	$262.30
Purchase #5	$212.82	4.375%	$222.1309	$222.13	$222.15	$222.10
Purchase #6	$19.42	3.153%	$20.0323	$20.03	$20.05	$20.00
Purchase #7	$114.53	9.593%	$125.5169	$125.52	$125.50	$125.50
7 purchase totals =	$941.03		$990.1303	$990.13	$990.10	$990.10