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	$169.82	5.664%	$179.4386	$179.44	$179.45	$179.40
Purchase #2	$123.28	13.620%	$140.0707	$140.07	$140.05	$140.10
Purchase #3	$121.38	5.400%	$127.9345	$127.93	$127.95	$127.90
Purchase #4	$104.90	4.563%	$109.6866	$109.69	$109.70	$109.70
Purchase #5	$180.95	10.487%	$199.9262	$199.93	$199.95	$199.90
Purchase #6	$69.86	5.807%	$73.9168	$73.92	$73.90	$73.90
Purchase #7	$127.39	9.396%	$139.3596	$139.36	$139.35	$139.40
7 purchase totals =	$897.58		$970.3330	$970.34	$970.35	$970.30