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	$235.95	12.276%	$264.9152	$264.92	$264.90	$264.90
Purchase #2	$152.63	13.231%	$172.8245	$172.82	$172.80	$172.80
Purchase #3	$62.58	12.853%	$70.6234	$70.62	$70.60	$70.60
Purchase #4	$160.63	7.189%	$172.1777	$172.18	$172.20	$172.20
Purchase #5	$136.65	4.507%	$142.8088	$142.81	$142.80	$142.80
Purchase #6	$98.83	13.607%	$112.2778	$112.28	$112.30	$112.30
Purchase #7	$7.97	6.417%	$8.4814	$8.48	$8.50	$8.50
7 purchase totals =	$855.24		$944.1088	$944.11	$944.10	$944.10