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	$52.59	12.503%	$59.1653	$59.17	$59.15	$59.20
Purchase #2	$67.43	5.702%	$71.2749	$71.27	$71.25	$71.30
Purchase #3	$221.50	9.451%	$242.434	$242.43	$242.45	$242.40
Purchase #4	$32.65	8.789%	$35.5196	$35.52	$35.50	$35.50
Purchase #5	$175.89	4.240%	$183.3477	$183.35	$183.35	$183.30
Purchase #6	$113.73	5.806%	$120.3332	$120.33	$120.35	$120.30
Purchase #7	$104.88	13.737%	$119.2874	$119.29	$119.30	$119.30
7 purchase totals =	$768.67		$831.3621	$831.36	$831.35	$831.30