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	$9.32	5.506%	$9.8332	$9.83	$9.85	$9.80
Purchase #2	$222.56	13.817%	$253.3111	$253.31	$253.30	$253.30
Purchase #3	$54.44	5.413%	$57.3868	$57.39	$57.40	$57.40
Purchase #4	$49.31	5.393%	$51.9693	$51.97	$51.95	$52.00
Purchase #5	$36.48	11.322%	$40.6103	$40.61	$40.60	$40.60
Purchase #6	$205.60	5.454%	$216.8134	$216.81	$216.80	$216.80
Purchase #7	$53.36	12.333%	$59.9409	$59.94	$59.95	$59.90
7 purchase totals =	$631.07		$689.8650	$689.86	$689.85	$689.80