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	$99.89	3.759%	$103.6449	$103.64	$103.65	$103.60
Purchase #2	$206.32	8.431%	$223.7148	$223.71	$223.70	$223.70
Purchase #3	$86.57	11.691%	$96.6909	$96.69	$96.70	$96.70
Purchase #4	$134.74	12.503%	$151.5865	$151.59	$151.60	$151.60
Purchase #5	$14.37	10.319%	$15.8528	$15.85	$15.85	$15.90
Purchase #6	$74.94	11.388%	$83.4742	$83.47	$83.45	$83.50
Purchase #7	$163.87	7.652%	$176.4093	$176.41	$176.40	$176.40
7 purchase totals =	$780.70		$851.3734	$851.36	$851.35	$851.40