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	$141.27	9.238%	$154.3205	$154.32	$154.30	$154.30
Purchase #2	$246.66	9.555%	$270.2284	$270.23	$270.25	$270.20
Purchase #3	$9.65	8.371%	$10.4578	$10.46	$10.45	$10.50
Purchase #4	$28.57	12.770%	$32.2184	$32.22	$32.20	$32.20
Purchase #5	$200.66	10.356%	$221.4403	$221.44	$221.45	$221.40
Purchase #6	$104.54	4.392%	$109.1314	$109.13	$109.15	$109.10
Purchase #7	$111.52	10.759%	$123.5184	$123.52	$123.50	$123.50
7 purchase totals =	$842.87		$921.3152	$921.32	$921.30	$921.20