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	$19.96	9.224%	$21.8011	$21.80	$21.80	$21.80
Purchase #2	$58.87	12.398%	$66.1687	$66.17	$66.15	$66.20
Purchase #3	$168.78	5.655%	$178.3245	$178.32	$178.30	$178.30
Purchase #4	$64.98	10.661%	$71.9075	$71.91	$71.90	$71.90
Purchase #5	$31.34	9.776%	$34.4038	$34.40	$34.40	$34.40
Purchase #6	$167.60	7.868%	$180.7868	$180.79	$180.80	$180.80
Purchase #7	$50.98	11.639%	$56.9136	$56.91	$56.90	$56.90
7 purchase totals =	$562.51		$610.3060	$610.30	$610.25	$610.30