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	$234.71	13.170%	$265.6213	$265.62	$265.60	$265.60
Purchase #2	$51.71	7.698%	$55.6906	$55.69	$55.70	$55.70
Purchase #3	$72.36	6.167%	$76.8224	$76.82	$76.80	$76.80
Purchase #4	$62.87	13.382%	$71.2833	$71.28	$71.30	$71.30
Purchase #5	$63.48	12.307%	$71.2925	$71.29	$71.30	$71.30
Purchase #6	$229.63	10.761%	$254.3405	$254.34	$254.35	$254.30
Purchase #7	$103.86	7.668%	$111.824	$111.82	$111.80	$111.80
7 purchase totals =	$818.62		$906.8746	$906.86	$906.85	$906.80