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	$131.86	4.811%	$138.2038	$138.20	$138.20	$138.20
Purchase #2	$142.66	3.371%	$147.4691	$147.47	$147.45	$147.50
Purchase #3	$231.33	10.420%	$255.4346	$255.43	$255.45	$255.40
Purchase #4	$107.80	5.165%	$113.3679	$113.37	$113.35	$113.40
Purchase #5	$245.40	5.845%	$259.7436	$259.74	$259.75	$259.70
Purchase #6	$82.86	11.738%	$92.5861	$92.59	$92.60	$92.60
Purchase #7	$86.63	3.291%	$89.481	$89.48	$89.50	$89.50
7 purchase totals =	$1,028.54		$1,096.2861	$1,096.28	$1,096.30	$1,096.30