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	$15.92	13.480%	$18.066	$18.07	$18.05	$18.10
Purchase #2	$215.50	8.826%	$234.52	$234.52	$234.50	$234.50
Purchase #3	$70.96	7.740%	$76.4523	$76.45	$76.45	$76.50
Purchase #4	$69.67	3.175%	$71.882	$71.88	$71.90	$71.90
Purchase #5	$235.47	11.715%	$263.0553	$263.06	$263.05	$263.10
Purchase #6	$19.34	4.865%	$20.2809	$20.28	$20.30	$20.30
Purchase #7	$16.74	11.259%	$18.6248	$18.62	$18.60	$18.60
7 purchase totals =	$643.60		$702.8813	$702.88	$702.85	$703.00