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	$137.48	8.216%	$148.7754	$148.78	$148.80	$148.80
Purchase #2	$226.94	12.646%	$255.6388	$255.64	$255.65	$255.60
Purchase #3	$26.87	6.293%	$28.5609	$28.56	$28.55	$28.60
Purchase #4	$82.44	9.646%	$90.3922	$90.39	$90.40	$90.40
Purchase #5	$11.72	12.441%	$13.1781	$13.18	$13.20	$13.20
Purchase #6	$57.82	11.382%	$64.4011	$64.40	$64.40	$64.40
Purchase #7	$144.65	12.287%	$162.4231	$162.42	$162.40	$162.40
7 purchase totals =	$687.92		$763.3696	$763.37	$763.40	$763.40