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	$157.83	8.644%	$171.4728	$171.47	$171.45	$171.50
Purchase #2	$168.92	12.828%	$190.5891	$190.59	$190.60	$190.60
Purchase #3	$144.78	6.384%	$154.0228	$154.02	$154.00	$154.00
Purchase #4	$136.25	7.515%	$146.4892	$146.49	$146.50	$146.50
Purchase #5	$168.84	7.104%	$180.8344	$180.83	$180.85	$180.80
Purchase #6	$173.31	10.620%	$191.7155	$191.72	$191.70	$191.70
Purchase #7	$7.43	11.168%	$8.2598	$8.26	$8.25	$8.30
7 purchase totals =	$957.36		$1,043.3836	$1,043.38	$1,043.35	$1,043.40