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	$96.67	8.868%	$105.2427	$105.24	$105.25	$105.20
Purchase #2	$88.51	8.753%	$96.2573	$96.26	$96.25	$96.30
Purchase #3	$153.56	12.528%	$172.798	$172.80	$172.80	$172.80
Purchase #4	$124.29	5.242%	$130.8053	$130.81	$130.80	$130.80
Purchase #5	$141.48	4.396%	$147.6995	$147.70	$147.70	$147.70
Purchase #6	$67.78	10.227%	$74.7119	$74.71	$74.70	$74.70
Purchase #7	$103.76	7.821%	$111.8751	$111.88	$111.90	$111.90
7 purchase totals =	$776.05		$839.3898	$839.40	$839.40	$839.40