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	$94.46	5.429%	$99.5882	$99.59	$99.60	$99.60
Purchase #2	$94.37	13.119%	$106.7504	$106.75	$106.75	$106.80
Purchase #3	$35.34	7.168%	$37.8732	$37.87	$37.85	$37.90
Purchase #4	$39.86	5.150%	$41.9128	$41.91	$41.90	$41.90
Purchase #5	$48.25	10.853%	$53.4866	$53.49	$53.50	$53.50
Purchase #6	$157.89	9.550%	$172.9685	$172.97	$172.95	$173.00
Purchase #7	$39.63	3.774%	$41.1256	$41.13	$41.15	$41.10
7 purchase totals =	$509.80		$553.7053	$553.71	$553.70	$553.80