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	$65.77	8.352%	$71.2631	$71.26	$71.25	$71.30
Purchase #2	$159.66	9.743%	$175.2157	$175.22	$175.20	$175.20
Purchase #3	$81.81	10.398%	$90.3166	$90.32	$90.30	$90.30
Purchase #4	$64.53	11.621%	$72.029	$72.03	$72.05	$72.00
Purchase #5	$168.30	5.667%	$177.8376	$177.84	$177.85	$177.80
Purchase #6	$12.78	4.301%	$13.3297	$13.33	$13.35	$13.30
Purchase #7	$142.98	11.264%	$159.0853	$159.09	$159.10	$159.10
7 purchase totals =	$695.83		$759.0770	$759.09	$759.10	$759.00