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	$29.83	10.238%	$32.884	$32.88	$32.90	$32.90
Purchase #2	$187.77	7.720%	$202.2658	$202.27	$202.25	$202.30
Purchase #3	$153.68	4.488%	$160.5772	$160.58	$160.60	$160.60
Purchase #4	$126.81	11.426%	$141.2993	$141.30	$141.30	$141.30
Purchase #5	$102.78	6.285%	$109.2397	$109.24	$109.25	$109.20
Purchase #6	$140.92	5.617%	$148.8355	$148.84	$148.85	$148.80
Purchase #7	$164.81	11.123%	$183.1418	$183.14	$183.15	$183.10
7 purchase totals =	$906.60		$978.2433	$978.25	$978.30	$978.20