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	$108.73	5.580%	$114.7971	$114.80	$114.80	$114.80
Purchase #2	$60.86	7.439%	$65.3874	$65.39	$65.40	$65.40
Purchase #3	$139.57	4.494%	$145.8423	$145.84	$145.85	$145.80
Purchase #4	$95.67	10.406%	$105.6254	$105.63	$105.65	$105.60
Purchase #5	$117.76	9.130%	$128.5115	$128.51	$128.50	$128.50
Purchase #6	$95.31	11.132%	$105.9199	$105.92	$105.90	$105.90
Purchase #7	$107.32	4.701%	$112.3651	$112.37	$112.35	$112.40
7 purchase totals =	$725.22		$778.4487	$778.46	$778.45	$778.40