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	$30.88	8.696%	$33.5653	$33.57	$33.55	$33.60
Purchase #2	$40.96	9.559%	$44.8754	$44.88	$44.90	$44.90
Purchase #3	$181.42	3.663%	$188.0654	$188.07	$188.05	$188.10
Purchase #4	$92.88	12.513%	$104.5021	$104.50	$104.50	$104.50
Purchase #5	$29.93	4.353%	$31.2329	$31.23	$31.25	$31.20
Purchase #6	$39.87	9.373%	$43.607	$43.61	$43.60	$43.60
Purchase #7	$91.69	7.561%	$98.6227	$98.62	$98.60	$98.60
7 purchase totals =	$507.63		$544.4708	$544.48	$544.45	$544.50