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	$20.98	5.442%	$22.1217	$22.12	$22.10	$22.10
Purchase #2	$57.60	5.354%	$60.6839	$60.68	$60.70	$60.70
Purchase #3	$183.45	9.412%	$200.7163	$200.72	$200.70	$200.70
Purchase #4	$105.53	7.596%	$113.5461	$113.55	$113.55	$113.50
Purchase #5	$153.47	7.750%	$165.3639	$165.36	$165.35	$165.40
Purchase #6	$53.85	11.325%	$59.9485	$59.95	$59.95	$59.90
Purchase #7	$123.57	5.398%	$130.2403	$130.24	$130.25	$130.20
7 purchase totals =	$698.45		$752.6207	$752.62	$752.60	$752.50