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	$142.90	9.508%	$156.4869	$156.49	$156.50	$156.50
Purchase #2	$45.43	3.778%	$47.1463	$47.15	$47.15	$47.10
Purchase #3	$69.79	4.362%	$72.8342	$72.83	$72.85	$72.80
Purchase #4	$199.58	4.230%	$208.0222	$208.02	$208.00	$208.00
Purchase #5	$134.85	4.842%	$141.3794	$141.38	$141.40	$141.40
Purchase #6	$139.50	6.576%	$148.6735	$148.67	$148.65	$148.70
Purchase #7	$172.28	7.529%	$185.251	$185.25	$185.25	$185.30
7 purchase totals =	$904.33		$959.7935	$959.79	$959.80	$959.80