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	$84.75	6.105%	$89.924	$89.92	$89.90	$89.90
Purchase #2	$54.58	11.364%	$60.7825	$60.78	$60.80	$60.80
Purchase #3	$51.79	13.340%	$58.6988	$58.70	$58.70	$58.70
Purchase #4	$232.89	10.280%	$256.8311	$256.83	$256.85	$256.80
Purchase #5	$34.37	12.419%	$38.6384	$38.64	$38.65	$38.60
Purchase #6	$92.54	8.370%	$100.2856	$100.29	$100.30	$100.30
Purchase #7	$90.36	3.810%	$93.8027	$93.80	$93.80	$93.80
7 purchase totals =	$641.28		$698.9631	$698.96	$699.00	$698.90