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	$105.39	12.286%	$118.3382	$118.34	$118.35	$118.30
Purchase #2	$73.79	6.565%	$78.6343	$78.63	$78.65	$78.60
Purchase #3	$50.60	13.855%	$57.6106	$57.61	$57.60	$57.60
Purchase #4	$149.90	3.388%	$154.9786	$154.98	$155.00	$155.00
Purchase #5	$54.44	8.863%	$59.265	$59.27	$59.25	$59.30
Purchase #6	$213.87	4.243%	$222.9445	$222.94	$222.95	$222.90
Purchase #7	$183.77	8.351%	$199.1166	$199.12	$199.10	$199.10
7 purchase totals =	$831.76		$890.8878	$890.89	$890.90	$890.80