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	$46.82	11.583%	$52.2432	$52.24	$52.25	$52.20
Purchase #2	$34.72	9.811%	$38.1264	$38.13	$38.15	$38.10
Purchase #3	$113.72	9.805%	$124.8702	$124.87	$124.85	$124.90
Purchase #4	$238.88	13.389%	$270.8636	$270.86	$270.85	$270.90
Purchase #5	$132.71	5.746%	$140.3355	$140.34	$140.35	$140.30
Purchase #6	$180.78	7.434%	$194.2192	$194.22	$194.20	$194.20
Purchase #7	$164.61	4.269%	$171.6372	$171.64	$171.65	$171.60
7 purchase totals =	$912.24		$992.2953	$992.30	$992.30	$992.20