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	$156.64	9.154%	$170.9788	$170.98	$171.00	$171.00
Purchase #2	$155.96	3.113%	$160.815	$160.82	$160.80	$160.80
Purchase #3	$131.49	5.281%	$138.434	$138.43	$138.45	$138.40
Purchase #4	$110.96	5.188%	$116.7166	$116.72	$116.70	$116.70
Purchase #5	$36.30	7.203%	$38.9147	$38.91	$38.90	$38.90
Purchase #6	$76.69	11.454%	$85.4741	$85.47	$85.45	$85.50
Purchase #7	$85.90	5.653%	$90.7559	$90.76	$90.75	$90.80
7 purchase totals =	$753.94		$802.0891	$802.09	$802.05	$802.10