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	$81.51	13.179%	$92.2522	$92.25	$92.25	$92.30
Purchase #2	$151.90	13.450%	$172.3306	$172.33	$172.35	$172.30
Purchase #3	$116.53	9.637%	$127.76	$127.76	$127.75	$127.80
Purchase #4	$195.44	10.669%	$216.2915	$216.29	$216.30	$216.30
Purchase #5	$88.72	13.388%	$100.5978	$100.60	$100.60	$100.60
Purchase #6	$213.78	5.506%	$225.5507	$225.55	$225.55	$225.60
Purchase #7	$56.49	12.469%	$63.5337	$63.53	$63.55	$63.50
7 purchase totals =	$904.37		$998.3165	$998.31	$998.35	$998.40