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	$70.86	13.660%	$80.5395	$80.54	$80.55	$80.50
Purchase #2	$241.81	12.124%	$271.127	$271.13	$271.15	$271.10
Purchase #3	$5.53	13.261%	$6.2633	$6.26	$6.25	$6.30
Purchase #4	$205.35	10.307%	$226.5154	$226.52	$226.50	$226.50
Purchase #5	$81.91	4.814%	$85.8531	$85.85	$85.85	$85.90
Purchase #6	$93.80	11.389%	$104.4829	$104.48	$104.50	$104.50
Purchase #7	$146.66	12.128%	$164.4469	$164.45	$164.45	$164.40
7 purchase totals =	$845.92		$939.2281	$939.23	$939.25	$939.20