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	$6.72	11.421%	$7.4875	$7.49	$7.50	$7.50
Purchase #2	$51.66	5.667%	$54.5876	$54.59	$54.60	$54.60
Purchase #3	$13.46	13.618%	$15.293	$15.29	$15.30	$15.30
Purchase #4	$83.63	6.400%	$88.9823	$88.98	$89.00	$89.00
Purchase #5	$36.43	3.238%	$37.6096	$37.61	$37.60	$37.60
Purchase #6	$148.85	4.873%	$156.1035	$156.10	$156.10	$156.10
Purchase #7	$206.94	6.739%	$220.8857	$220.89	$220.90	$220.90
7 purchase totals =	$547.69		$580.9492	$580.95	$581.00	$581.00