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	$20.93	3.677%	$21.6996	$21.70	$21.70	$21.70
Purchase #2	$96.41	13.504%	$109.4292	$109.43	$109.45	$109.40
Purchase #3	$122.30	8.137%	$132.2516	$132.25	$132.25	$132.30
Purchase #4	$164.25	12.840%	$185.3397	$185.34	$185.35	$185.30
Purchase #5	$72.53	6.300%	$77.0994	$77.10	$77.10	$77.10
Purchase #6	$59.71	12.626%	$67.249	$67.25	$67.25	$67.20
Purchase #7	$75.34	11.258%	$83.8218	$83.82	$83.80	$83.80
7 purchase totals =	$611.47		$676.8903	$676.89	$676.90	$676.80