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	$103.59	4.369%	$108.1158	$108.12	$108.10	$108.10
Purchase #2	$137.74	3.329%	$142.3254	$142.33	$142.35	$142.30
Purchase #3	$230.34	3.506%	$238.4157	$238.42	$238.40	$238.40
Purchase #4	$76.37	11.610%	$85.2366	$85.24	$85.25	$85.20
Purchase #5	$96.51	8.825%	$105.027	$105.03	$105.05	$105.00
Purchase #6	$166.92	8.330%	$180.8244	$180.82	$180.80	$180.80
Purchase #7	$20.39	11.539%	$22.7428	$22.74	$22.75	$22.70
7 purchase totals =	$831.86		$882.6877	$882.70	$882.70	$882.50