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	$9.31	11.142%	$10.3473	$10.35	$10.35	$10.30
Purchase #2	$222.73	12.296%	$250.1169	$250.12	$250.10	$250.10
Purchase #3	$13.42	11.342%	$14.9421	$14.94	$14.95	$14.90
Purchase #4	$148.76	13.641%	$169.0524	$169.05	$169.05	$169.10
Purchase #5	$82.45	6.663%	$87.9436	$87.94	$87.95	$87.90
Purchase #6	$65.38	5.671%	$69.0877	$69.09	$69.10	$69.10
Purchase #7	$53.55	10.276%	$59.0528	$59.05	$59.05	$59.10
7 purchase totals =	$595.60		$660.5428	$660.54	$660.55	$660.50