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	$120.94	6.113%	$128.3331	$128.33	$128.35	$128.30
Purchase #2	$84.83	5.603%	$89.583	$89.58	$89.60	$89.60
Purchase #3	$119.48	10.145%	$131.6012	$131.60	$131.60	$131.60
Purchase #4	$55.47	6.402%	$59.0212	$59.02	$59.00	$59.00
Purchase #5	$171.76	9.120%	$187.4245	$187.42	$187.40	$187.40
Purchase #6	$136.55	3.775%	$141.7048	$141.70	$141.70	$141.70
Purchase #7	$117.87	8.169%	$127.4988	$127.50	$127.50	$127.50
7 purchase totals =	$806.90		$865.1666	$865.15	$865.15	$865.10