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	$83.42	7.602%	$89.7616	$89.76	$89.75	$89.80
Purchase #2	$54.50	8.695%	$59.2388	$59.24	$59.25	$59.20
Purchase #3	$249.63	6.595%	$266.0931	$266.09	$266.10	$266.10
Purchase #4	$169.38	5.163%	$178.1251	$178.13	$178.15	$178.10
Purchase #5	$144.69	3.648%	$149.9683	$149.97	$149.95	$150.00
Purchase #6	$234.42	11.472%	$261.3127	$261.31	$261.30	$261.30
Purchase #7	$113.54	4.765%	$118.9502	$118.95	$118.95	$119.00
7 purchase totals =	$1,049.58		$1,123.4498	$1,123.45	$1,123.45	$1,123.50