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	$34.89	13.580%	$39.6281	$39.63	$39.65	$39.60
Purchase #2	$211.70	6.384%	$225.2149	$225.21	$225.20	$225.20
Purchase #3	$200.36	8.863%	$218.1179	$218.12	$218.10	$218.10
Purchase #4	$39.56	12.494%	$44.5026	$44.50	$44.50	$44.50
Purchase #5	$142.45	11.498%	$158.8289	$158.83	$158.85	$158.80
Purchase #6	$122.63	11.846%	$137.1567	$137.16	$137.15	$137.20
Purchase #7	$126.73	3.672%	$131.3835	$131.38	$131.40	$131.40
7 purchase totals =	$878.32		$954.8326	$954.83	$954.85	$954.80