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	$170.97	6.355%	$181.8351	$181.84	$181.85	$181.80
Purchase #2	$239.57	13.448%	$271.7874	$271.79	$271.80	$271.80
Purchase #3	$233.51	5.184%	$245.6152	$245.62	$245.60	$245.60
Purchase #4	$92.25	6.310%	$98.071	$98.07	$98.05	$98.10
Purchase #5	$215.29	13.574%	$244.5135	$244.51	$244.50	$244.50
Purchase #6	$233.61	10.872%	$259.0081	$259.01	$259.00	$259.00
Purchase #7	$100.69	10.725%	$111.489	$111.49	$111.50	$111.50
7 purchase totals =	$1,285.89		$1,412.3193	$1,412.33	$1,412.30	$1,412.30