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	$141.26	7.130%	$151.3318	$151.33	$151.35	$151.30
Purchase #2	$29.84	8.826%	$32.4737	$32.47	$32.45	$32.50
Purchase #3	$217.67	8.341%	$235.8259	$235.83	$235.85	$235.80
Purchase #4	$19.74	5.675%	$20.8602	$20.86	$20.85	$20.90
Purchase #5	$86.74	5.465%	$91.4803	$91.48	$91.50	$91.50
Purchase #6	$20.74	3.514%	$21.4688	$21.47	$21.45	$21.50
Purchase #7	$15.37	13.467%	$17.4399	$17.44	$17.45	$17.40
7 purchase totals =	$531.36		$570.8806	$570.88	$570.90	$570.90