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	$84.32	7.659%	$90.7781	$90.78	$90.80	$90.80
Purchase #2	$214.38	10.689%	$237.2951	$237.30	$237.30	$237.30
Purchase #3	$86.89	5.127%	$91.3449	$91.34	$91.35	$91.30
Purchase #4	$36.55	4.706%	$38.27	$38.27	$38.25	$38.30
Purchase #5	$216.25	8.365%	$234.3393	$234.34	$234.35	$234.30
Purchase #6	$17.87	13.513%	$20.2848	$20.28	$20.30	$20.30
Purchase #7	$99.77	5.310%	$105.0678	$105.07	$105.05	$105.10
7 purchase totals =	$756.03		$817.3800	$817.38	$817.40	$817.40