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	$206.26	13.330%	$233.7545	$233.75	$233.75	$233.80
Purchase #2	$73.29	3.212%	$75.6441	$75.64	$75.65	$75.60
Purchase #3	$121.83	12.742%	$137.3536	$137.35	$137.35	$137.40
Purchase #4	$222.36	12.870%	$250.9777	$250.98	$251.00	$251.00
Purchase #5	$107.73	3.812%	$111.8367	$111.84	$111.85	$111.80
Purchase #6	$211.61	5.698%	$223.6675	$223.67	$223.65	$223.70
Purchase #7	$100.63	11.338%	$112.0394	$112.04	$112.05	$112.00
7 purchase totals =	$1,043.71		$1,145.2735	$1,145.27	$1,145.30	$1,145.30