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	$12.35	3.307%	$12.7584	$12.76	$12.75	$12.80
Purchase #2	$187.80	6.484%	$199.977	$199.98	$200.00	$200.00
Purchase #3	$182.79	8.786%	$198.8499	$198.85	$198.85	$198.80
Purchase #4	$191.91	7.315%	$205.9482	$205.95	$205.95	$205.90
Purchase #5	$41.83	9.617%	$45.8528	$45.85	$45.85	$45.90
Purchase #6	$36.64	11.676%	$40.9181	$40.92	$40.90	$40.90
Purchase #7	$93.38	3.687%	$96.8229	$96.82	$96.80	$96.80
7 purchase totals =	$746.70		$801.1273	$801.13	$801.10	$801.10