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	$134.35	8.857%	$146.2494	$146.25	$146.25	$146.20
Purchase #2	$113.59	9.444%	$124.3174	$124.32	$124.30	$124.30
Purchase #3	$74.81	5.273%	$78.7547	$78.75	$78.75	$78.80
Purchase #4	$150.58	11.218%	$167.4721	$167.47	$167.45	$167.50
Purchase #5	$129.75	7.526%	$139.515	$139.52	$139.50	$139.50
Purchase #6	$177.41	10.740%	$196.4638	$196.46	$196.45	$196.50
Purchase #7	$49.92	3.443%	$51.6387	$51.64	$51.65	$51.60
7 purchase totals =	$830.41		$904.4111	$904.41	$904.35	$904.40