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	$35.68	13.112%	$40.3584	$40.36	$40.35	$40.40
Purchase #2	$82.41	10.474%	$91.0416	$91.04	$91.05	$91.00
Purchase #3	$182.39	7.635%	$196.3155	$196.32	$196.30	$196.30
Purchase #4	$12.26	9.491%	$13.4236	$13.42	$13.40	$13.40
Purchase #5	$47.64	9.711%	$52.2663	$52.27	$52.25	$52.30
Purchase #6	$172.48	5.654%	$182.232	$182.23	$182.25	$182.20
Purchase #7	$45.77	8.846%	$49.8188	$49.82	$49.80	$49.80
7 purchase totals =	$578.63		$625.4562	$625.46	$625.40	$625.40