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	$108.31	6.544%	$115.3978	$115.40	$115.40	$115.40
Purchase #2	$58.56	13.589%	$66.5177	$66.52	$66.50	$66.50
Purchase #3	$72.59	13.380%	$82.3025	$82.30	$82.30	$82.30
Purchase #4	$61.35	5.313%	$64.6095	$64.61	$64.60	$64.60
Purchase #5	$190.39	11.849%	$212.9493	$212.95	$212.95	$212.90
Purchase #6	$72.79	6.423%	$77.4653	$77.47	$77.45	$77.50
Purchase #7	$178.66	5.381%	$188.2737	$188.27	$188.25	$188.30
7 purchase totals =	$742.65		$807.5158	$807.52	$807.45	$807.50