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	$43.51	13.498%	$49.383	$49.38	$49.40	$49.40
Purchase #2	$55.52	12.247%	$62.3195	$62.32	$62.30	$62.30
Purchase #3	$66.68	13.711%	$75.8225	$75.82	$75.80	$75.80
Purchase #4	$77.57	6.502%	$82.6136	$82.61	$82.60	$82.60
Purchase #5	$97.63	7.495%	$104.9474	$104.95	$104.95	$104.90
Purchase #6	$129.73	5.135%	$136.3916	$136.39	$136.40	$136.40
Purchase #7	$81.96	9.413%	$89.6749	$89.67	$89.65	$89.70
7 purchase totals =	$552.60		$601.1525	$601.14	$601.10	$601.10