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	$224.80	13.865%	$255.9685	$255.97	$255.95	$256.00
Purchase #2	$27.31	5.440%	$28.7957	$28.80	$28.80	$28.80
Purchase #3	$187.89	9.344%	$205.4464	$205.45	$205.45	$205.40
Purchase #4	$37.56	5.621%	$39.6712	$39.67	$39.65	$39.70
Purchase #5	$84.68	5.630%	$89.4475	$89.45	$89.45	$89.40
Purchase #6	$182.36	9.290%	$199.3012	$199.30	$199.30	$199.30
Purchase #7	$24.26	12.451%	$27.2806	$27.28	$27.30	$27.30
7 purchase totals =	$768.86		$845.9111	$845.92	$845.90	$845.90