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	$43.56	11.371%	$48.5132	$48.51	$48.50	$48.50
Purchase #2	$80.93	11.211%	$90.0031	$90.00	$90.00	$90.00
Purchase #3	$158.36	11.482%	$176.5429	$176.54	$176.55	$176.50
Purchase #4	$112.66	3.799%	$116.94	$116.94	$116.95	$116.90
Purchase #5	$141.92	7.810%	$153.004	$153.00	$153.00	$153.00
Purchase #6	$109.54	11.791%	$122.4559	$122.46	$122.45	$122.50
Purchase #7	$121.94	5.284%	$128.3833	$128.38	$128.40	$128.40
7 purchase totals =	$768.91		$835.8424	$835.83	$835.85	$835.80