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	$137.92	4.537%	$144.1774	$144.18	$144.20	$144.20
Purchase #2	$142.87	6.464%	$152.1051	$152.11	$152.10	$152.10
Purchase #3	$134.51	7.690%	$144.8538	$144.85	$144.85	$144.90
Purchase #4	$49.64	6.474%	$52.8537	$52.85	$52.85	$52.90
Purchase #5	$47.58	10.478%	$52.5654	$52.57	$52.55	$52.60
Purchase #6	$110.56	7.370%	$118.7083	$118.71	$118.70	$118.70
Purchase #7	$12.82	10.872%	$14.2138	$14.21	$14.20	$14.20
7 purchase totals =	$635.90		$679.4775	$679.48	$679.45	$679.60