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	$187.81	6.131%	$199.3246	$199.32	$199.30	$199.30
Purchase #2	$70.25	11.854%	$78.5774	$78.58	$78.60	$78.60
Purchase #3	$81.33	7.369%	$87.3232	$87.32	$87.30	$87.30
Purchase #4	$37.67	7.568%	$40.5209	$40.52	$40.50	$40.50
Purchase #5	$243.54	5.664%	$257.3341	$257.33	$257.35	$257.30
Purchase #6	$91.88	4.688%	$96.1873	$96.19	$96.20	$96.20
Purchase #7	$127.51	8.483%	$138.3267	$138.33	$138.35	$138.30
7 purchase totals =	$839.99		$897.5942	$897.59	$897.60	$897.50