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	$200.72	11.504%	$223.8108	$223.81	$223.80	$223.80
Purchase #2	$152.71	11.383%	$170.093	$170.09	$170.10	$170.10
Purchase #3	$100.84	12.369%	$113.3129	$113.31	$113.30	$113.30
Purchase #4	$37.34	13.605%	$42.4201	$42.42	$42.40	$42.40
Purchase #5	$59.50	7.470%	$63.9447	$63.94	$63.95	$63.90
Purchase #6	$204.56	7.123%	$219.1308	$219.13	$219.15	$219.10
Purchase #7	$228.63	10.120%	$251.7674	$251.77	$251.75	$251.80
7 purchase totals =	$984.30		$1,084.4797	$1,084.47	$1,084.45	$1,084.40