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	$19.42	4.196%	$20.2349	$20.23	$20.25	$20.20
Purchase #2	$70.98	10.294%	$78.2867	$78.29	$78.30	$78.30
Purchase #3	$147.54	12.235%	$165.5915	$165.59	$165.60	$165.60
Purchase #4	$64.34	11.610%	$71.8099	$71.81	$71.80	$71.80
Purchase #5	$94.81	13.730%	$107.8274	$107.83	$107.85	$107.80
Purchase #6	$246.72	9.225%	$269.4799	$269.48	$269.50	$269.50
Purchase #7	$81.35	12.709%	$91.6888	$91.69	$91.70	$91.70
7 purchase totals =	$725.16		$804.9191	$804.92	$805.00	$804.90