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	$168.43	9.440%	$184.3298	$184.33	$184.35	$184.30
Purchase #2	$57.55	3.545%	$59.5901	$59.59	$59.60	$59.60
Purchase #3	$165.40	11.776%	$184.8775	$184.88	$184.90	$184.90
Purchase #4	$17.72	12.175%	$19.8774	$19.88	$19.90	$19.90
Purchase #5	$138.54	3.318%	$143.1368	$143.14	$143.15	$143.10
Purchase #6	$42.55	8.688%	$46.2467	$46.25	$46.25	$46.20
Purchase #7	$44.90	7.265%	$48.162	$48.16	$48.15	$48.20
7 purchase totals =	$635.09		$686.2203	$686.23	$686.30	$686.20