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	$59.46	11.541%	$66.3223	$66.32	$66.30	$66.30
Purchase #2	$78.32	13.339%	$88.7671	$88.77	$88.75	$88.80
Purchase #3	$197.51	9.218%	$215.7165	$215.72	$215.70	$215.70
Purchase #4	$82.76	10.525%	$91.4705	$91.47	$91.45	$91.50
Purchase #5	$36.25	9.391%	$39.6542	$39.65	$39.65	$39.70
Purchase #6	$118.86	3.646%	$123.1936	$123.19	$123.20	$123.20
Purchase #7	$172.37	5.516%	$181.8779	$181.88	$181.90	$181.90
7 purchase totals =	$745.53		$807.0021	$807.00	$806.95	$807.10