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	$44.38	13.291%	$50.2785	$50.28	$50.30	$50.30
Purchase #2	$141.97	6.794%	$151.6154	$151.62	$151.60	$151.60
Purchase #3	$239.61	13.296%	$271.4685	$271.47	$271.45	$271.50
Purchase #4	$6.37	11.863%	$7.1257	$7.13	$7.15	$7.10
Purchase #5	$137.68	7.319%	$147.7568	$147.76	$147.75	$147.80
Purchase #6	$32.86	13.155%	$37.1827	$37.18	$37.20	$37.20
Purchase #7	$221.91	5.443%	$233.9886	$233.99	$234.00	$234.00
7 purchase totals =	$824.78		$899.4162	$899.43	$899.45	$899.50