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	$150.46	10.402%	$166.1108	$166.11	$166.10	$166.10
Purchase #2	$106.42	9.139%	$116.1457	$116.15	$116.15	$116.10
Purchase #3	$29.26	10.762%	$32.409	$32.41	$32.40	$32.40
Purchase #4	$123.41	12.859%	$139.2793	$139.28	$139.30	$139.30
Purchase #5	$11.39	9.587%	$12.482	$12.48	$12.50	$12.50
Purchase #6	$239.77	11.471%	$267.274	$267.27	$267.25	$267.30
Purchase #7	$75.63	4.378%	$78.9411	$78.94	$78.95	$78.90
7 purchase totals =	$736.34		$812.6419	$812.64	$812.65	$812.60