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	$89.32	6.254%	$94.9061	$94.91	$94.90	$94.90
Purchase #2	$117.90	12.218%	$132.305	$132.31	$132.30	$132.30
Purchase #3	$205.28	9.294%	$224.3587	$224.36	$224.35	$224.40
Purchase #4	$190.57	3.109%	$196.4948	$196.49	$196.50	$196.50
Purchase #5	$36.49	13.570%	$41.4417	$41.44	$41.45	$41.40
Purchase #6	$195.52	9.636%	$214.3603	$214.36	$214.35	$214.40
Purchase #7	$50.73	7.203%	$54.3841	$54.38	$54.40	$54.40
7 purchase totals =	$885.81		$958.2507	$958.25	$958.25	$958.30