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	$29.72	5.423%	$31.3317	$31.33	$31.35	$31.30
Purchase #2	$205.84	7.629%	$221.5435	$221.54	$221.55	$221.50
Purchase #3	$115.63	13.301%	$131.0099	$131.01	$131.00	$131.00
Purchase #4	$117.34	12.596%	$132.1201	$132.12	$132.10	$132.10
Purchase #5	$180.83	8.433%	$196.0794	$196.08	$196.10	$196.10
Purchase #6	$52.98	3.843%	$55.016	$55.02	$55.00	$55.00
Purchase #7	$234.69	7.160%	$251.4938	$251.49	$251.50	$251.50
7 purchase totals =	$937.03		$1,018.5944	$1,018.59	$1,018.60	$1,018.50