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	$160.46	12.553%	$180.6025	$180.60	$180.60	$180.60
Purchase #2	$188.61	11.272%	$209.8701	$209.87	$209.85	$209.90
Purchase #3	$40.35	12.591%	$45.4305	$45.43	$45.45	$45.40
Purchase #4	$45.54	8.276%	$49.3089	$49.31	$49.30	$49.30
Purchase #5	$129.96	7.593%	$139.8279	$139.83	$139.85	$139.80
Purchase #6	$201.52	13.454%	$228.6325	$228.63	$228.65	$228.60
Purchase #7	$132.33	10.365%	$146.046	$146.05	$146.05	$146.00
7 purchase totals =	$898.77		$999.7184	$999.72	$999.75	$999.60