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	$18.49	11.500%	$20.6164	$20.62	$20.60	$20.60
Purchase #2	$60.54	12.112%	$67.8726	$67.87	$67.85	$67.90
Purchase #3	$215.29	11.534%	$240.1215	$240.12	$240.10	$240.10
Purchase #4	$19.61	10.484%	$21.6659	$21.67	$21.65	$21.70
Purchase #5	$139.86	4.395%	$146.0068	$146.01	$146.00	$146.00
Purchase #6	$73.79	11.753%	$82.4625	$82.46	$82.45	$82.50
Purchase #7	$234.42	6.710%	$250.1496	$250.15	$250.15	$250.10
7 purchase totals =	$762.00		$828.8953	$828.90	$828.80	$828.90