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	$209.92	8.764%	$228.3174	$228.32	$228.30	$228.30
Purchase #2	$130.73	6.156%	$138.7777	$138.78	$138.80	$138.80
Purchase #3	$235.76	13.692%	$268.0403	$268.04	$268.05	$268.00
Purchase #4	$93.39	6.477%	$99.4389	$99.44	$99.45	$99.40
Purchase #5	$154.39	4.322%	$161.0627	$161.06	$161.05	$161.10
Purchase #6	$95.83	8.638%	$104.1078	$104.11	$104.10	$104.10
Purchase #7	$231.87	10.315%	$255.7874	$255.79	$255.80	$255.80
7 purchase totals =	$1,151.89		$1,255.5322	$1,255.54	$1,255.55	$1,255.50