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	$89.57	12.656%	$100.906	$100.91	$100.90	$100.90
Purchase #2	$216.32	11.696%	$241.6208	$241.62	$241.60	$241.60
Purchase #3	$29.47	8.689%	$32.0306	$32.03	$32.05	$32.00
Purchase #4	$111.47	10.708%	$123.4062	$123.41	$123.40	$123.40
Purchase #5	$132.37	3.279%	$136.7104	$136.71	$136.70	$136.70
Purchase #6	$103.75	5.716%	$109.6804	$109.68	$109.70	$109.70
Purchase #7	$133.67	11.751%	$149.3776	$149.38	$149.40	$149.40
7 purchase totals =	$816.62		$893.7320	$893.74	$893.75	$893.70