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	$35.92	9.870%	$39.4653	$39.47	$39.45	$39.50
Purchase #2	$110.34	10.650%	$122.0912	$122.09	$122.10	$122.10
Purchase #3	$197.91	5.119%	$208.041	$208.04	$208.05	$208.00
Purchase #4	$102.65	8.739%	$111.6206	$111.62	$111.60	$111.60
Purchase #5	$80.75	13.330%	$91.514	$91.51	$91.50	$91.50
Purchase #6	$245.45	7.443%	$263.7188	$263.72	$263.70	$263.70
Purchase #7	$232.77	13.271%	$263.6609	$263.66	$263.65	$263.70
7 purchase totals =	$1,005.79		$1,100.1118	$1,100.11	$1,100.05	$1,100.10