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	$249.82	12.186%	$280.2631	$280.26	$280.25	$280.30
Purchase #2	$49.91	3.154%	$51.4842	$51.48	$51.50	$51.50
Purchase #3	$208.50	11.476%	$232.4275	$232.43	$232.45	$232.40
Purchase #4	$97.32	4.333%	$101.5369	$101.54	$101.55	$101.50
Purchase #5	$79.67	10.811%	$88.2831	$88.28	$88.30	$88.30
Purchase #6	$103.88	7.138%	$111.295	$111.30	$111.30	$111.30
Purchase #7	$210.31	3.170%	$216.9768	$216.98	$217.00	$217.00
7 purchase totals =	$999.41		$1,082.2666	$1,082.27	$1,082.35	$1,082.30