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	$45.30	10.539%	$50.0742	$50.07	$50.05	$50.10
Purchase #2	$162.41	5.793%	$171.8184	$171.82	$171.80	$171.80
Purchase #3	$78.33	6.403%	$83.3455	$83.35	$83.35	$83.30
Purchase #4	$50.27	8.636%	$54.6113	$54.61	$54.60	$54.60
Purchase #5	$131.51	8.289%	$142.4109	$142.41	$142.40	$142.40
Purchase #6	$82.61	8.546%	$89.6699	$89.67	$89.65	$89.70
Purchase #7	$181.92	12.128%	$203.9833	$203.98	$204.00	$204.00
7 purchase totals =	$732.35		$795.9135	$795.91	$795.85	$795.90