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	$143.92	8.107%	$155.5876	$155.59	$155.60	$155.60
Purchase #2	$88.53	5.486%	$93.3868	$93.39	$93.40	$93.40
Purchase #3	$128.65	10.710%	$142.4284	$142.43	$142.45	$142.40
Purchase #4	$109.90	7.248%	$117.8656	$117.87	$117.85	$117.90
Purchase #5	$118.33	7.334%	$127.0083	$127.01	$127.00	$127.00
Purchase #6	$17.44	3.708%	$18.0867	$18.09	$18.10	$18.10
Purchase #7	$76.56	13.309%	$86.7494	$86.75	$86.75	$86.70
7 purchase totals =	$683.33		$741.1128	$741.13	$741.15	$741.10