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	$234.30	3.843%	$243.3041	$243.30	$243.30	$243.30
Purchase #2	$87.73	4.640%	$91.8007	$91.80	$91.80	$91.80
Purchase #3	$45.66	13.872%	$51.994	$51.99	$52.00	$52.00
Purchase #4	$34.81	10.756%	$38.5542	$38.55	$38.55	$38.60
Purchase #5	$150.57	3.839%	$156.3504	$156.35	$156.35	$156.40
Purchase #6	$85.46	5.817%	$90.4312	$90.43	$90.45	$90.40
Purchase #7	$157.72	6.831%	$168.4939	$168.49	$168.50	$168.50
7 purchase totals =	$796.25		$840.9285	$840.91	$840.95	$841.00