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	$134.98	8.361%	$146.2657	$146.27	$146.25	$146.30
Purchase #2	$121.62	8.469%	$131.92	$131.92	$131.90	$131.90
Purchase #3	$19.98	4.513%	$20.8817	$20.88	$20.90	$20.90
Purchase #4	$151.98	13.871%	$173.0611	$173.06	$173.05	$173.10
Purchase #5	$236.64	5.855%	$250.4953	$250.50	$250.50	$250.50
Purchase #6	$45.50	9.786%	$49.9526	$49.95	$49.95	$50.00
Purchase #7	$95.71	4.238%	$99.7662	$99.77	$99.75	$99.80
7 purchase totals =	$806.41		$872.3426	$872.35	$872.30	$872.50