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	$58.98	10.246%	$65.0231	$65.02	$65.00	$65.00
Purchase #2	$96.98	6.321%	$103.1101	$103.11	$103.10	$103.10
Purchase #3	$233.66	10.647%	$258.5378	$258.54	$258.55	$258.50
Purchase #4	$112.43	7.568%	$120.9387	$120.94	$120.95	$120.90
Purchase #5	$72.70	12.665%	$81.9075	$81.91	$81.90	$81.90
Purchase #6	$79.49	13.339%	$90.0932	$90.09	$90.10	$90.10
Purchase #7	$62.26	5.180%	$65.4851	$65.49	$65.50	$65.50
7 purchase totals =	$716.50		$785.0955	$785.10	$785.10	$785.00