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	$140.33	11.140%	$155.9628	$155.96	$155.95	$156.00
Purchase #2	$55.97	6.507%	$59.612	$59.61	$59.60	$59.60
Purchase #3	$100.59	8.840%	$109.4822	$109.48	$109.50	$109.50
Purchase #4	$178.89	6.432%	$190.3962	$190.40	$190.40	$190.40
Purchase #5	$224.56	12.706%	$253.0926	$253.09	$253.10	$253.10
Purchase #6	$78.65	10.640%	$87.0184	$87.02	$87.00	$87.00
Purchase #7	$28.53	13.183%	$32.2911	$32.29	$32.30	$32.30
7 purchase totals =	$807.52		$887.8553	$887.85	$887.85	$887.90