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	$75.30	9.516%	$82.4655	$82.47	$82.45	$82.50
Purchase #2	$222.76	9.810%	$244.6128	$244.61	$244.60	$244.60
Purchase #3	$96.44	8.163%	$104.3124	$104.31	$104.30	$104.30
Purchase #4	$54.92	12.554%	$61.8147	$61.81	$61.80	$61.80
Purchase #5	$98.68	4.709%	$103.3268	$103.33	$103.35	$103.30
Purchase #6	$144.49	11.763%	$161.4864	$161.49	$161.50	$161.50
Purchase #7	$32.47	13.520%	$36.8599	$36.86	$36.85	$36.90
7 purchase totals =	$725.06		$794.8785	$794.88	$794.85	$794.90