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	$14.38	10.473%	$15.886	$15.89	$15.90	$15.90
Purchase #2	$15.66	10.515%	$17.3066	$17.31	$17.30	$17.30
Purchase #3	$87.59	3.775%	$90.8965	$90.90	$90.90	$90.90
Purchase #4	$38.56	13.220%	$43.6576	$43.66	$43.65	$43.70
Purchase #5	$150.57	7.519%	$161.8914	$161.89	$161.90	$161.90
Purchase #6	$64.28	5.304%	$67.6894	$67.69	$67.70	$67.70
Purchase #7	$130.99	8.685%	$142.3665	$142.37	$142.35	$142.40
7 purchase totals =	$502.03		$539.6940	$539.71	$539.70	$539.80