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	$205.56	11.348%	$228.8869	$228.89	$228.90	$228.90
Purchase #2	$119.86	11.739%	$133.9304	$133.93	$133.95	$133.90
Purchase #3	$148.97	5.801%	$157.6117	$157.61	$157.60	$157.60
Purchase #4	$218.53	11.466%	$243.5866	$243.59	$243.60	$243.60
Purchase #5	$147.50	3.516%	$152.6861	$152.69	$152.70	$152.70
Purchase #6	$9.65	12.787%	$10.8839	$10.88	$10.90	$10.90
Purchase #7	$12.45	6.857%	$13.3037	$13.30	$13.30	$13.30
7 purchase totals =	$862.52		$940.8893	$940.89	$940.95	$940.90