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	$211.46	8.475%	$229.3812	$229.38	$229.40	$229.40
Purchase #2	$201.91	11.728%	$225.59	$225.59	$225.60	$225.60
Purchase #3	$133.73	7.102%	$143.2275	$143.23	$143.25	$143.20
Purchase #4	$16.35	12.664%	$18.4206	$18.42	$18.40	$18.40
Purchase #5	$34.71	8.368%	$37.6145	$37.61	$37.60	$37.60
Purchase #6	$73.27	13.122%	$82.8845	$82.88	$82.90	$82.90
Purchase #7	$134.49	11.584%	$150.0693	$150.07	$150.05	$150.10
7 purchase totals =	$805.92		$887.1876	$887.18	$887.20	$887.20