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	$88.76	13.345%	$100.605	$100.61	$100.60	$100.60
Purchase #2	$82.77	3.351%	$85.5436	$85.54	$85.55	$85.50
Purchase #3	$83.87	9.609%	$91.9291	$91.93	$91.95	$91.90
Purchase #4	$172.58	11.573%	$192.5527	$192.55	$192.55	$192.60
Purchase #5	$75.46	9.455%	$82.5947	$82.59	$82.60	$82.60
Purchase #6	$242.71	13.366%	$275.1506	$275.15	$275.15	$275.20
Purchase #7	$176.46	6.824%	$188.5016	$188.50	$188.50	$188.50
7 purchase totals =	$922.61		$1,016.8773	$1,016.87	$1,016.90	$1,016.90