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	$33.50	8.381%	$36.3076	$36.31	$36.30	$36.30
Purchase #2	$92.96	11.485%	$103.6365	$103.64	$103.65	$103.60
Purchase #3	$73.53	7.239%	$78.8528	$78.85	$78.85	$78.90
Purchase #4	$86.26	4.696%	$90.3108	$90.31	$90.30	$90.30
Purchase #5	$137.55	9.271%	$150.3023	$150.30	$150.30	$150.30
Purchase #6	$204.72	7.846%	$220.7823	$220.78	$220.80	$220.80
Purchase #7	$133.84	3.241%	$138.1778	$138.18	$138.20	$138.20
7 purchase totals =	$762.36		$818.3701	$818.37	$818.40	$818.40