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	$73.89	11.775%	$82.5905	$82.59	$82.60	$82.60
Purchase #2	$189.62	10.117%	$208.8039	$208.80	$208.80	$208.80
Purchase #3	$24.41	3.191%	$25.1889	$25.19	$25.20	$25.20
Purchase #4	$87.55	9.474%	$95.8445	$95.84	$95.85	$95.80
Purchase #5	$91.58	9.546%	$100.3222	$100.32	$100.30	$100.30
Purchase #6	$48.31	7.561%	$51.9627	$51.96	$51.95	$52.00
Purchase #7	$75.33	3.715%	$78.1285	$78.13	$78.15	$78.10
7 purchase totals =	$590.69		$642.8412	$642.83	$642.85	$642.80