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	$17.35	12.301%	$19.4842	$19.48	$19.50	$19.50
Purchase #2	$131.33	10.271%	$144.8189	$144.82	$144.80	$144.80
Purchase #3	$21.45	13.309%	$24.3048	$24.30	$24.30	$24.30
Purchase #4	$191.26	10.627%	$211.5852	$211.59	$211.60	$211.60
Purchase #5	$37.88	12.399%	$42.5767	$42.58	$42.60	$42.60
Purchase #6	$100.40	5.414%	$105.8357	$105.84	$105.85	$105.80
Purchase #7	$51.68	12.672%	$58.2289	$58.23	$58.25	$58.20
7 purchase totals =	$551.35		$606.8344	$606.84	$606.90	$606.80