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	$51.59	11.309%	$57.4243	$57.42	$57.40	$57.40
Purchase #2	$224.75	13.549%	$255.2014	$255.20	$255.20	$255.20
Purchase #3	$42.69	11.786%	$47.7214	$47.72	$47.70	$47.70
Purchase #4	$169.88	7.772%	$183.0831	$183.08	$183.10	$183.10
Purchase #5	$232.98	13.752%	$265.0194	$265.02	$265.00	$265.00
Purchase #6	$60.39	12.407%	$67.8826	$67.88	$67.90	$67.90
Purchase #7	$70.81	11.171%	$78.7202	$78.72	$78.70	$78.70
7 purchase totals =	$853.09		$955.0524	$955.04	$955.00	$955.00