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	$59.43	11.621%	$66.3364	$66.34	$66.35	$66.30
Purchase #2	$37.69	6.358%	$40.0863	$40.09	$40.10	$40.10
Purchase #3	$162.56	8.327%	$176.0964	$176.10	$176.10	$176.10
Purchase #4	$89.79	8.597%	$97.5092	$97.51	$97.50	$97.50
Purchase #5	$58.56	13.441%	$66.431	$66.43	$66.45	$66.40
Purchase #6	$46.46	10.750%	$51.4545	$51.45	$51.45	$51.50
Purchase #7	$59.46	6.665%	$63.423	$63.42	$63.40	$63.40
7 purchase totals =	$513.95		$561.3368	$561.34	$561.35	$561.30