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	$83.44	8.790%	$90.7744	$90.77	$90.75	$90.80
Purchase #2	$42.48	3.457%	$43.9485	$43.95	$43.95	$43.90
Purchase #3	$53.44	10.630%	$59.1207	$59.12	$59.10	$59.10
Purchase #4	$35.85	6.108%	$38.0397	$38.04	$38.05	$38.00
Purchase #5	$106.95	8.723%	$116.2792	$116.28	$116.30	$116.30
Purchase #6	$244.97	8.652%	$266.1648	$266.16	$266.15	$266.20
Purchase #7	$41.89	13.785%	$47.6645	$47.66	$47.65	$47.70
7 purchase totals =	$609.02		$661.9918	$661.98	$661.95	$662.00