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	$70.42	11.642%	$78.6183	$78.62	$78.60	$78.60
Purchase #2	$114.40	7.703%	$123.2122	$123.21	$123.20	$123.20
Purchase #3	$87.38	8.139%	$94.4919	$94.49	$94.50	$94.50
Purchase #4	$61.58	4.452%	$64.3215	$64.32	$64.30	$64.30
Purchase #5	$39.54	12.128%	$44.3354	$44.34	$44.35	$44.30
Purchase #6	$93.62	6.756%	$99.945	$99.95	$99.95	$99.90
Purchase #7	$79.90	11.661%	$89.2171	$89.22	$89.20	$89.20
7 purchase totals =	$546.84		$594.1414	$594.15	$594.10	$594.00