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	$85.90	5.130%	$90.3067	$90.31	$90.30	$90.30
Purchase #2	$231.62	4.537%	$242.1286	$242.13	$242.15	$242.10
Purchase #3	$62.84	6.864%	$67.1533	$67.15	$67.15	$67.20
Purchase #4	$140.88	6.647%	$150.2443	$150.24	$150.25	$150.20
Purchase #5	$89.43	3.554%	$92.6083	$92.61	$92.60	$92.60
Purchase #6	$161.79	9.136%	$176.5711	$176.57	$176.55	$176.60
Purchase #7	$66.37	8.731%	$72.1648	$72.16	$72.15	$72.20
7 purchase totals =	$838.83		$891.1771	$891.17	$891.15	$891.20