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	$236.89	7.842%	$255.4669	$255.47	$255.45	$255.50
Purchase #2	$150.69	11.162%	$167.51	$167.51	$167.50	$167.50
Purchase #3	$63.59	4.341%	$66.3504	$66.35	$66.35	$66.40
Purchase #4	$61.80	10.569%	$68.3316	$68.33	$68.35	$68.30
Purchase #5	$172.93	7.705%	$186.2543	$186.25	$186.25	$186.30
Purchase #6	$26.95	11.727%	$30.1104	$30.11	$30.10	$30.10
Purchase #7	$202.37	11.450%	$225.5414	$225.54	$225.55	$225.50
7 purchase totals =	$915.22		$999.5650	$999.56	$999.55	$999.60