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	$80.84	11.464%	$90.1075	$90.11	$90.10	$90.10
Purchase #2	$234.53	4.704%	$245.5623	$245.56	$245.55	$245.60
Purchase #3	$110.94	8.427%	$120.2889	$120.29	$120.30	$120.30
Purchase #4	$126.54	12.724%	$142.6409	$142.64	$142.65	$142.60
Purchase #5	$70.41	10.727%	$77.9629	$77.96	$77.95	$78.00
Purchase #6	$101.90	9.226%	$111.3013	$111.30	$111.30	$111.30
Purchase #7	$204.95	3.330%	$211.7748	$211.77	$211.75	$211.80
7 purchase totals =	$930.11		$999.6386	$999.63	$999.60	$999.70