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	$56.27	5.421%	$59.3204	$59.32	$59.30	$59.30
Purchase #2	$176.79	5.218%	$186.0149	$186.01	$186.00	$186.00
Purchase #3	$247.38	6.780%	$264.1524	$264.15	$264.15	$264.20
Purchase #4	$121.60	4.390%	$126.9382	$126.94	$126.95	$126.90
Purchase #5	$63.61	12.363%	$71.4741	$71.47	$71.45	$71.50
Purchase #6	$41.72	8.429%	$45.2366	$45.24	$45.25	$45.20
Purchase #7	$205.43	10.614%	$227.2343	$227.23	$227.25	$227.20
7 purchase totals =	$912.80		$980.3709	$980.36	$980.35	$980.30