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	$24.73	9.771%	$27.1464	$27.15	$27.15	$27.10
Purchase #2	$154.43	5.398%	$162.7661	$162.77	$162.75	$162.80
Purchase #3	$12.39	6.822%	$13.2352	$13.24	$13.25	$13.20
Purchase #4	$25.89	10.241%	$28.5414	$28.54	$28.55	$28.50
Purchase #5	$176.51	13.497%	$200.3336	$200.33	$200.35	$200.30
Purchase #6	$104.85	4.833%	$109.9174	$109.92	$109.90	$109.90
Purchase #7	$117.39	8.440%	$127.2977	$127.30	$127.30	$127.30
7 purchase totals =	$616.19		$669.2378	$669.25	$669.25	$669.10