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	$47.47	4.547%	$49.6285	$49.63	$49.65	$49.60
Purchase #2	$101.99	10.823%	$113.0284	$113.03	$113.05	$113.00
Purchase #3	$12.95	4.453%	$13.5267	$13.53	$13.55	$13.50
Purchase #4	$156.83	9.228%	$171.3023	$171.30	$171.30	$171.30
Purchase #5	$51.70	7.521%	$55.5884	$55.59	$55.60	$55.60
Purchase #6	$223.53	13.453%	$253.6015	$253.60	$253.60	$253.60
Purchase #7	$72.51	13.302%	$82.1553	$82.16	$82.15	$82.20
7 purchase totals =	$666.98		$738.8311	$738.84	$738.90	$738.80