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	$28.59	10.183%	$31.5013	$31.50	$31.50	$31.50
Purchase #2	$59.53	9.559%	$65.2205	$65.22	$65.20	$65.20
Purchase #3	$84.75	7.227%	$90.8749	$90.87	$90.85	$90.90
Purchase #4	$91.45	7.469%	$98.2804	$98.28	$98.30	$98.30
Purchase #5	$235.63	8.707%	$256.1463	$256.15	$256.15	$256.10
Purchase #6	$236.92	3.153%	$244.3901	$244.39	$244.40	$244.40
Purchase #7	$50.61	11.753%	$56.5582	$56.56	$56.55	$56.60
7 purchase totals =	$787.48		$842.9717	$842.97	$842.95	$843.00