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	$29.31	5.692%	$30.9783	$30.98	$31.00	$31.00
Purchase #2	$87.72	4.425%	$91.6016	$91.60	$91.60	$91.60
Purchase #3	$156.34	3.172%	$161.2991	$161.30	$161.30	$161.30
Purchase #4	$95.80	5.745%	$101.3037	$101.30	$101.30	$101.30
Purchase #5	$116.48	9.766%	$127.8554	$127.86	$127.85	$127.90
Purchase #6	$155.67	5.740%	$164.6055	$164.61	$164.60	$164.60
Purchase #7	$5.61	12.679%	$6.3213	$6.32	$6.30	$6.30
7 purchase totals =	$646.93		$683.9649	$683.97	$683.95	$684.00