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	$92.65	7.474%	$99.5747	$99.57	$99.55	$99.60
Purchase #2	$85.70	5.272%	$90.2181	$90.22	$90.20	$90.20
Purchase #3	$123.50	8.716%	$134.2643	$134.26	$134.25	$134.30
Purchase #4	$163.48	7.825%	$176.2723	$176.27	$176.25	$176.30
Purchase #5	$90.32	12.867%	$101.9415	$101.94	$101.95	$101.90
Purchase #6	$68.86	11.221%	$76.5868	$76.59	$76.60	$76.60
Purchase #7	$29.43	11.759%	$32.8907	$32.89	$32.90	$32.90
7 purchase totals =	$653.94		$711.7484	$711.74	$711.70	$711.80