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	$48.71	7.823%	$52.5206	$52.52	$52.50	$52.50
Purchase #2	$214.32	6.483%	$228.2144	$228.21	$228.20	$228.20
Purchase #3	$109.33	7.241%	$117.2466	$117.25	$117.25	$117.20
Purchase #4	$113.92	4.663%	$119.2321	$119.23	$119.25	$119.20
Purchase #5	$25.32	8.555%	$27.4861	$27.49	$27.50	$27.50
Purchase #6	$29.52	10.592%	$32.6468	$32.65	$32.65	$32.60
Purchase #7	$78.35	13.437%	$88.8779	$88.88	$88.90	$88.90
7 purchase totals =	$619.47		$666.2245	$666.23	$666.25	$666.10