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	$101.59	5.171%	$106.8432	$106.84	$106.85	$106.80
Purchase #2	$54.87	9.167%	$59.8999	$59.90	$59.90	$59.90
Purchase #3	$86.63	3.654%	$89.7955	$89.80	$89.80	$89.80
Purchase #4	$66.34	11.578%	$74.0208	$74.02	$74.00	$74.00
Purchase #5	$205.78	10.709%	$227.817	$227.82	$227.80	$227.80
Purchase #6	$48.64	9.326%	$53.1762	$53.18	$53.20	$53.20
Purchase #7	$70.84	11.434%	$78.9398	$78.94	$78.95	$78.90
7 purchase totals =	$634.69		$690.4924	$690.50	$690.50	$690.40