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	$45.87	3.869%	$47.6447	$47.64	$47.65	$47.60
Purchase #2	$131.93	13.861%	$150.2168	$150.22	$150.20	$150.20
Purchase #3	$119.40	9.640%	$130.9102	$130.91	$130.90	$130.90
Purchase #4	$71.34	9.453%	$78.0838	$78.08	$78.10	$78.10
Purchase #5	$82.56	8.262%	$89.3811	$89.38	$89.40	$89.40
Purchase #6	$152.41	13.717%	$173.3161	$173.32	$173.30	$173.30
Purchase #7	$82.77	5.398%	$87.2379	$87.24	$87.25	$87.20
7 purchase totals =	$686.28		$756.7906	$756.79	$756.80	$756.70