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	$34.63	7.440%	$37.2065	$37.21	$37.20	$37.20
Purchase #2	$154.75	6.335%	$164.5534	$164.55	$164.55	$164.60
Purchase #3	$99.53	11.582%	$111.0576	$111.06	$111.05	$111.10
Purchase #4	$211.28	9.762%	$231.9052	$231.91	$231.90	$231.90
Purchase #5	$43.58	4.621%	$45.5938	$45.59	$45.60	$45.60
Purchase #6	$35.60	10.335%	$39.2793	$39.28	$39.30	$39.30
Purchase #7	$174.32	10.811%	$193.1657	$193.17	$193.15	$193.20
7 purchase totals =	$753.69		$822.7615	$822.77	$822.75	$822.90