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	$136.53	5.697%	$144.3081	$144.31	$144.30	$144.30
Purchase #2	$91.82	7.698%	$98.8883	$98.89	$98.90	$98.90
Purchase #3	$9.61	13.573%	$10.9144	$10.91	$10.90	$10.90
Purchase #4	$40.59	6.411%	$43.1922	$43.19	$43.20	$43.20
Purchase #5	$127.61	10.611%	$141.1507	$141.15	$141.15	$141.20
Purchase #6	$232.61	11.374%	$259.0671	$259.07	$259.05	$259.10
Purchase #7	$34.87	5.660%	$36.8436	$36.84	$36.85	$36.80
7 purchase totals =	$673.64		$734.3644	$734.36	$734.35	$734.40