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	$21.59	6.604%	$23.0158	$23.02	$23.00	$23.00
Purchase #2	$144.62	5.697%	$152.859	$152.86	$152.85	$152.90
Purchase #3	$74.76	4.779%	$78.3328	$78.33	$78.35	$78.30
Purchase #4	$130.74	10.617%	$144.6207	$144.62	$144.60	$144.60
Purchase #5	$210.73	13.359%	$238.8814	$238.88	$238.90	$238.90
Purchase #6	$194.80	8.446%	$211.2528	$211.25	$211.25	$211.30
Purchase #7	$92.44	3.122%	$95.326	$95.33	$95.35	$95.30
7 purchase totals =	$869.68		$944.2885	$944.29	$944.30	$944.30