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	$29.89	11.835%	$33.4275	$33.43	$33.45	$33.40
Purchase #2	$79.40	13.291%	$89.9531	$89.95	$89.95	$90.00
Purchase #3	$223.64	8.116%	$241.7906	$241.79	$241.80	$241.80
Purchase #4	$127.83	7.174%	$137.0005	$137.00	$137.00	$137.00
Purchase #5	$210.47	4.292%	$219.5034	$219.50	$219.50	$219.50
Purchase #6	$210.75	12.684%	$237.4815	$237.48	$237.50	$237.50
Purchase #7	$236.51	11.746%	$264.2905	$264.29	$264.30	$264.30
7 purchase totals =	$1,118.49		$1,223.4471	$1,223.44	$1,223.50	$1,223.50