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	$100.37	12.104%	$112.5188	$112.52	$112.50	$112.50
Purchase #2	$232.52	10.368%	$256.6277	$256.63	$256.65	$256.60
Purchase #3	$132.94	6.343%	$141.3724	$141.37	$141.35	$141.40
Purchase #4	$86.47	10.454%	$95.5096	$95.51	$95.50	$95.50
Purchase #5	$216.96	5.691%	$229.3072	$229.31	$229.30	$229.30
Purchase #6	$18.68	3.672%	$19.3659	$19.37	$19.35	$19.40
Purchase #7	$162.99	12.474%	$183.3214	$183.32	$183.30	$183.30
7 purchase totals =	$950.93		$1,038.0230	$1,038.03	$1,037.95	$1,038.00