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	$102.84	8.254%	$111.3284	$111.33	$111.35	$111.30
Purchase #2	$71.64	10.301%	$79.0196	$79.02	$79.00	$79.00
Purchase #3	$35.52	6.761%	$37.9215	$37.92	$37.90	$37.90
Purchase #4	$48.67	9.266%	$53.1798	$53.18	$53.20	$53.20
Purchase #5	$121.89	13.482%	$138.3232	$138.32	$138.30	$138.30
Purchase #6	$217.97	13.556%	$247.518	$247.52	$247.50	$247.50
Purchase #7	$172.29	9.791%	$189.1589	$189.16	$189.15	$189.20
7 purchase totals =	$770.82		$856.4494	$856.45	$856.40	$856.40