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	$20.88	4.202%	$21.7574	$21.76	$21.75	$21.80
Purchase #2	$71.32	6.309%	$75.8196	$75.82	$75.80	$75.80
Purchase #3	$52.84	9.340%	$57.7753	$57.78	$57.80	$57.80
Purchase #4	$175.39	13.225%	$198.5853	$198.59	$198.60	$198.60
Purchase #5	$152.25	5.444%	$160.5385	$160.54	$160.55	$160.50
Purchase #6	$29.93	12.127%	$33.5596	$33.56	$33.55	$33.60
Purchase #7	$147.81	6.582%	$157.5389	$157.54	$157.55	$157.50
7 purchase totals =	$650.42		$705.5746	$705.59	$705.60	$705.60