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	$150.95	11.451%	$168.2353	$168.24	$168.25	$168.20
Purchase #2	$146.38	13.188%	$165.6846	$165.68	$165.70	$165.70
Purchase #3	$97.98	7.216%	$105.0502	$105.05	$105.05	$105.10
Purchase #4	$68.39	7.716%	$73.667	$73.67	$73.65	$73.70
Purchase #5	$144.48	9.285%	$157.895	$157.90	$157.90	$157.90
Purchase #6	$106.61	4.639%	$111.5556	$111.56	$111.55	$111.60
Purchase #7	$15.55	8.750%	$16.9106	$16.91	$16.90	$16.90
7 purchase totals =	$730.34		$798.9983	$799.01	$799.00	$799.10