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	$101.92	6.842%	$108.8934	$108.89	$108.90	$108.90
Purchase #2	$144.60	7.765%	$155.8282	$155.83	$155.85	$155.80
Purchase #3	$127.67	10.243%	$140.7472	$140.75	$140.75	$140.70
Purchase #4	$117.81	5.767%	$124.6041	$124.60	$124.60	$124.60
Purchase #5	$25.66	6.149%	$27.2378	$27.24	$27.25	$27.20
Purchase #6	$230.50	8.519%	$250.1363	$250.14	$250.15	$250.10
Purchase #7	$41.32	6.214%	$43.8876	$43.89	$43.90	$43.90
7 purchase totals =	$789.48		$851.3346	$851.34	$851.40	$851.20