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	$119.85	6.680%	$127.856	$127.86	$127.85	$127.90
Purchase #2	$79.97	12.374%	$89.8655	$89.87	$89.85	$89.90
Purchase #3	$14.83	11.216%	$16.4933	$16.49	$16.50	$16.50
Purchase #4	$133.47	12.732%	$150.4634	$150.46	$150.45	$150.50
Purchase #5	$56.77	5.539%	$59.9145	$59.91	$59.90	$59.90
Purchase #6	$73.90	12.638%	$83.2395	$83.24	$83.25	$83.20
Purchase #7	$162.58	12.283%	$182.5497	$182.55	$182.55	$182.50
7 purchase totals =	$641.37		$710.3819	$710.38	$710.35	$710.40