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	$71.88	12.824%	$81.0979	$81.10	$81.10	$81.10
Purchase #2	$122.28	9.698%	$134.1387	$134.14	$134.15	$134.10
Purchase #3	$221.60	9.705%	$243.1063	$243.11	$243.10	$243.10
Purchase #4	$165.53	12.260%	$185.824	$185.82	$185.80	$185.80
Purchase #5	$111.65	10.603%	$123.4882	$123.49	$123.50	$123.50
Purchase #6	$6.52	11.578%	$7.2749	$7.27	$7.25	$7.30
Purchase #7	$149.81	6.121%	$158.9799	$158.98	$159.00	$159.00
7 purchase totals =	$849.27		$933.9099	$933.91	$933.90	$933.90