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	$170.48	9.198%	$186.1608	$186.16	$186.15	$186.20
Purchase #2	$71.61	10.572%	$79.1806	$79.18	$79.20	$79.20
Purchase #3	$107.90	10.850%	$119.6072	$119.61	$119.60	$119.60
Purchase #4	$79.86	13.808%	$90.8871	$90.89	$90.90	$90.90
Purchase #5	$125.68	9.464%	$137.5744	$137.57	$137.55	$137.60
Purchase #6	$235.80	3.615%	$244.3242	$244.32	$244.30	$244.30
Purchase #7	$148.59	10.489%	$164.1756	$164.18	$164.20	$164.20
7 purchase totals =	$939.92		$1,021.9099	$1,021.91	$1,021.90	$1,022.00