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	$39.64	4.613%	$41.4686	$41.47	$41.45	$41.50
Purchase #2	$134.74	12.118%	$151.0678	$151.07	$151.05	$151.10
Purchase #3	$35.86	8.322%	$38.8443	$38.84	$38.85	$38.80
Purchase #4	$138.35	6.156%	$146.8668	$146.87	$146.85	$146.90
Purchase #5	$170.87	10.682%	$189.1223	$189.12	$189.10	$189.10
Purchase #6	$27.89	13.158%	$31.5598	$31.56	$31.55	$31.60
Purchase #7	$94.28	4.547%	$98.5669	$98.57	$98.55	$98.60
7 purchase totals =	$641.63		$697.4965	$697.50	$697.40	$697.60