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	$17.40	8.205%	$18.8277	$18.83	$18.85	$18.80
Purchase #2	$39.71	12.187%	$44.5495	$44.55	$44.55	$44.50
Purchase #3	$169.97	12.180%	$190.6723	$190.67	$190.65	$190.70
Purchase #4	$161.63	4.104%	$168.2633	$168.26	$168.25	$168.30
Purchase #5	$224.71	11.633%	$250.8505	$250.85	$250.85	$250.90
Purchase #6	$63.52	5.395%	$66.9469	$66.95	$66.95	$66.90
Purchase #7	$102.36	9.281%	$111.86	$111.86	$111.85	$111.90
7 purchase totals =	$779.30		$851.9702	$851.97	$851.95	$852.00