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	$83.48	8.763%	$90.7954	$90.80	$90.80	$90.80
Purchase #2	$54.72	9.316%	$59.8177	$59.82	$59.80	$59.80
Purchase #3	$5.98	4.248%	$6.234	$6.23	$6.25	$6.20
Purchase #4	$31.91	12.842%	$36.0079	$36.01	$36.00	$36.00
Purchase #5	$159.89	5.164%	$168.1467	$168.15	$168.15	$168.10
Purchase #6	$208.93	5.492%	$220.4044	$220.40	$220.40	$220.40
Purchase #7	$37.91	12.348%	$42.5911	$42.59	$42.60	$42.60
7 purchase totals =	$582.82		$623.9972	$624.00	$624.00	$623.90