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	$92.37	8.766%	$100.4672	$100.47	$100.45	$100.50
Purchase #2	$55.53	5.216%	$58.4264	$58.43	$58.45	$58.40
Purchase #3	$121.85	13.376%	$138.1487	$138.15	$138.15	$138.10
Purchase #4	$34.80	11.827%	$38.9158	$38.92	$38.90	$38.90
Purchase #5	$204.35	7.398%	$219.4678	$219.47	$219.45	$219.50
Purchase #6	$232.35	5.254%	$244.5577	$244.56	$244.55	$244.60
Purchase #7	$197.37	9.708%	$216.5307	$216.53	$216.55	$216.50
7 purchase totals =	$938.62		$1,016.5143	$1,016.53	$1,016.50	$1,016.50