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	$38.83	8.736%	$42.2222	$42.22	$42.20	$42.20
Purchase #2	$164.36	7.393%	$176.5111	$176.51	$176.50	$176.50
Purchase #3	$131.86	13.297%	$149.3934	$149.39	$149.40	$149.40
Purchase #4	$177.46	4.762%	$185.9106	$185.91	$185.90	$185.90
Purchase #5	$35.84	8.486%	$38.8814	$38.88	$38.90	$38.90
Purchase #6	$50.76	10.288%	$55.9822	$55.98	$56.00	$56.00
Purchase #7	$142.87	9.767%	$156.8241	$156.82	$156.80	$156.80
7 purchase totals =	$741.98		$805.7250	$805.71	$805.70	$805.70