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	$37.53	7.314%	$40.2749	$40.27	$40.25	$40.30
Purchase #2	$217.92	10.539%	$240.8866	$240.89	$240.90	$240.90
Purchase #3	$74.55	8.363%	$80.7846	$80.78	$80.80	$80.80
Purchase #4	$70.99	4.175%	$73.9538	$73.95	$73.95	$74.00
Purchase #5	$85.57	3.814%	$88.8336	$88.83	$88.85	$88.80
Purchase #6	$46.47	12.807%	$52.4214	$52.42	$52.40	$52.40
Purchase #7	$141.91	9.517%	$155.4156	$155.42	$155.40	$155.40
7 purchase totals =	$674.94		$732.5705	$732.56	$732.55	$732.60