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	$42.66	12.318%	$47.9149	$47.91	$47.90	$47.90
Purchase #2	$76.90	10.722%	$85.1452	$85.15	$85.15	$85.10
Purchase #3	$172.39	11.452%	$192.1321	$192.13	$192.15	$192.10
Purchase #4	$150.54	3.329%	$155.5515	$155.55	$155.55	$155.60
Purchase #5	$131.77	10.622%	$145.7666	$145.77	$145.75	$145.80
Purchase #6	$36.89	12.861%	$41.6344	$41.63	$41.65	$41.60
Purchase #7	$168.97	11.372%	$188.1853	$188.19	$188.20	$188.20
7 purchase totals =	$780.12		$856.3300	$856.33	$856.35	$856.30