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	$38.79	12.639%	$43.6927	$43.69	$43.70	$43.70
Purchase #2	$232.59	13.463%	$263.9036	$263.90	$263.90	$263.90
Purchase #3	$233.97	11.763%	$261.4919	$261.49	$261.50	$261.50
Purchase #4	$234.72	8.647%	$255.0162	$255.02	$255.00	$255.00
Purchase #5	$81.55	11.792%	$91.1664	$91.17	$91.15	$91.20
Purchase #6	$192.62	10.507%	$212.8586	$212.86	$212.85	$212.90
Purchase #7	$88.33	13.606%	$100.3482	$100.35	$100.35	$100.30
7 purchase totals =	$1,102.57		$1,228.4776	$1,228.48	$1,228.45	$1,228.50