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	$39.64	5.692%	$41.8963	$41.90	$41.90	$41.90
Purchase #2	$139.53	11.252%	$155.2299	$155.23	$155.25	$155.20
Purchase #3	$99.33	9.256%	$108.524	$108.52	$108.50	$108.50
Purchase #4	$199.89	5.261%	$210.4062	$210.41	$210.40	$210.40
Purchase #5	$221.45	13.458%	$251.2527	$251.25	$251.25	$251.30
Purchase #6	$106.53	5.528%	$112.419	$112.42	$112.40	$112.40
Purchase #7	$111.59	4.205%	$116.2824	$116.28	$116.30	$116.30
7 purchase totals =	$917.96		$996.0105	$996.01	$996.00	$996.00