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	$155.42	5.767%	$164.3831	$164.38	$164.40	$164.40
Purchase #2	$200.72	11.669%	$224.142	$224.14	$224.15	$224.10
Purchase #3	$195.56	6.154%	$207.5948	$207.59	$207.60	$207.60
Purchase #4	$129.89	11.164%	$144.3909	$144.39	$144.40	$144.40
Purchase #5	$24.87	7.872%	$26.8278	$26.83	$26.85	$26.80
Purchase #6	$80.32	12.188%	$90.1094	$90.11	$90.10	$90.10
Purchase #7	$38.88	13.115%	$43.9791	$43.98	$44.00	$44.00
7 purchase totals =	$825.66		$901.4271	$901.42	$901.50	$901.40