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	$187.51	13.801%	$213.3883	$213.39	$213.40	$213.40
Purchase #2	$238.83	9.527%	$261.5833	$261.58	$261.60	$261.60
Purchase #3	$122.47	3.720%	$127.0259	$127.03	$127.05	$127.00
Purchase #4	$90.56	9.749%	$99.3887	$99.39	$99.40	$99.40
Purchase #5	$106.34	6.201%	$112.9341	$112.93	$112.95	$112.90
Purchase #6	$238.93	5.208%	$251.3735	$251.37	$251.35	$251.40
Purchase #7	$224.44	8.278%	$243.0191	$243.02	$243.00	$243.00
7 purchase totals =	$1,209.08		$1,308.7129	$1,308.71	$1,308.75	$1,308.70