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	$131.66	6.569%	$140.3087	$140.31	$140.30	$140.30
Purchase #2	$198.99	9.804%	$218.499	$218.50	$218.50	$218.50
Purchase #3	$154.48	7.172%	$165.5593	$165.56	$165.55	$165.60
Purchase #4	$49.77	8.762%	$54.1308	$54.13	$54.15	$54.10
Purchase #5	$133.75	12.269%	$150.1598	$150.16	$150.15	$150.20
Purchase #6	$17.83	5.569%	$18.823	$18.82	$18.80	$18.80
Purchase #7	$70.43	13.749%	$80.1134	$80.11	$80.10	$80.10
7 purchase totals =	$756.91		$827.5940	$827.59	$827.55	$827.60