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	$146.49	12.512%	$164.8188	$164.82	$164.80	$164.80
Purchase #2	$51.39	6.189%	$54.5705	$54.57	$54.55	$54.60
Purchase #3	$48.30	4.714%	$50.5769	$50.58	$50.60	$50.60
Purchase #4	$61.44	7.841%	$66.2575	$66.26	$66.25	$66.30
Purchase #5	$95.36	4.427%	$99.5816	$99.58	$99.60	$99.60
Purchase #6	$242.66	8.166%	$262.4756	$262.48	$262.50	$262.50
Purchase #7	$170.81	12.272%	$191.7718	$191.77	$191.75	$191.80
7 purchase totals =	$816.45		$890.0527	$890.06	$890.05	$890.20