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	$209.91	12.728%	$236.6273	$236.63	$236.65	$236.60
Purchase #2	$34.49	8.381%	$37.3806	$37.38	$37.40	$37.40
Purchase #3	$120.58	5.660%	$127.4048	$127.40	$127.40	$127.40
Purchase #4	$185.25	10.860%	$205.3682	$205.37	$205.35	$205.40
Purchase #5	$41.94	13.302%	$47.5189	$47.52	$47.50	$47.50
Purchase #6	$92.63	11.649%	$103.4205	$103.42	$103.40	$103.40
Purchase #7	$148.50	11.539%	$165.6354	$165.64	$165.65	$165.60
7 purchase totals =	$833.30		$923.3557	$923.36	$923.35	$923.30