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	$234.52	11.413%	$261.2858	$261.29	$261.30	$261.30
Purchase #2	$199.64	12.818%	$225.2299	$225.23	$225.25	$225.20
Purchase #3	$90.45	10.528%	$99.9726	$99.97	$99.95	$100.00
Purchase #4	$147.37	13.535%	$167.3165	$167.32	$167.30	$167.30
Purchase #5	$217.48	3.697%	$225.5202	$225.52	$225.50	$225.50
Purchase #6	$247.52	5.569%	$261.3044	$261.30	$261.30	$261.30
Purchase #7	$75.46	7.146%	$80.8524	$80.85	$80.85	$80.90
7 purchase totals =	$1,212.44		$1,321.4818	$1,321.48	$1,321.45	$1,321.50