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	$72.89	7.482%	$78.3436	$78.34	$78.35	$78.30
Purchase #2	$29.69	5.401%	$31.2936	$31.29	$31.30	$31.30
Purchase #3	$138.35	8.393%	$149.9617	$149.96	$149.95	$150.00
Purchase #4	$107.32	11.858%	$120.046	$120.05	$120.05	$120.00
Purchase #5	$67.92	4.164%	$70.7482	$70.75	$70.75	$70.70
Purchase #6	$246.28	7.581%	$264.9505	$264.95	$264.95	$265.00
Purchase #7	$231.30	13.622%	$262.8077	$262.81	$262.80	$262.80
7 purchase totals =	$893.75		$978.1513	$978.15	$978.15	$978.10