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	$82.81	5.676%	$87.5103	$87.51	$87.50	$87.50
Purchase #2	$156.59	6.545%	$166.8388	$166.84	$166.85	$166.80
Purchase #3	$248.83	3.689%	$258.0093	$258.01	$258.00	$258.00
Purchase #4	$143.85	5.189%	$151.3144	$151.31	$151.30	$151.30
Purchase #5	$64.82	11.559%	$72.3125	$72.31	$72.30	$72.30
Purchase #6	$219.81	9.271%	$240.1886	$240.19	$240.20	$240.20
Purchase #7	$155.73	8.361%	$168.7506	$168.75	$168.75	$168.80
7 purchase totals =	$1,072.44		$1,144.9245	$1,144.92	$1,144.90	$1,144.90