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	$25.95	9.423%	$28.3953	$28.40	$28.40	$28.40
Purchase #2	$30.54	5.858%	$32.329	$32.33	$32.35	$32.30
Purchase #3	$127.93	6.662%	$136.4527	$136.45	$136.45	$136.50
Purchase #4	$93.40	10.663%	$103.3592	$103.36	$103.35	$103.40
Purchase #5	$69.33	13.108%	$78.4178	$78.42	$78.40	$78.40
Purchase #6	$112.86	11.575%	$125.9235	$125.92	$125.90	$125.90
Purchase #7	$93.81	12.382%	$105.4256	$105.43	$105.45	$105.40
7 purchase totals =	$553.82		$610.3031	$610.31	$610.30	$610.30