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	$228.64	5.171%	$240.463	$240.46	$240.45	$240.50
Purchase #2	$197.78	6.144%	$209.9316	$209.93	$209.95	$209.90
Purchase #3	$71.47	8.144%	$77.2905	$77.29	$77.30	$77.30
Purchase #4	$39.65	12.405%	$44.5686	$44.57	$44.55	$44.60
Purchase #5	$63.39	4.784%	$66.4226	$66.42	$66.40	$66.40
Purchase #6	$81.56	10.578%	$90.1874	$90.19	$90.20	$90.20
Purchase #7	$243.86	3.179%	$251.6123	$251.61	$251.60	$251.60
7 purchase totals =	$926.35		$980.4760	$980.47	$980.45	$980.50