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	$40.82	13.696%	$46.4107	$46.41	$46.40	$46.40
Purchase #2	$66.89	7.767%	$72.0853	$72.09	$72.10	$72.10
Purchase #3	$44.88	10.155%	$49.4376	$49.44	$49.45	$49.40
Purchase #4	$192.82	9.324%	$210.7985	$210.80	$210.80	$210.80
Purchase #5	$83.94	7.428%	$90.1751	$90.18	$90.20	$90.20
Purchase #6	$171.98	3.669%	$178.2899	$178.29	$178.30	$178.30
Purchase #7	$161.98	10.802%	$179.4771	$179.48	$179.50	$179.50
7 purchase totals =	$763.31		$826.6742	$826.69	$826.75	$826.70