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	$29.71	7.735%	$32.0081	$32.01	$32.00	$32.00
Purchase #2	$43.71	3.126%	$45.0764	$45.08	$45.10	$45.10
Purchase #3	$143.60	13.357%	$162.7807	$162.78	$162.80	$162.80
Purchase #4	$145.84	10.339%	$160.9184	$160.92	$160.90	$160.90
Purchase #5	$6.78	10.281%	$7.4771	$7.48	$7.50	$7.50
Purchase #6	$233.29	6.583%	$248.6475	$248.65	$248.65	$248.60
Purchase #7	$117.90	11.647%	$131.6318	$131.63	$131.65	$131.60
7 purchase totals =	$720.83		$788.5400	$788.55	$788.60	$788.50