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	$203.77	13.424%	$231.1241	$231.12	$231.10	$231.10
Purchase #2	$171.59	12.289%	$192.6767	$192.68	$192.70	$192.70
Purchase #3	$111.30	7.330%	$119.4583	$119.46	$119.45	$119.50
Purchase #4	$207.59	11.341%	$231.1328	$231.13	$231.15	$231.10
Purchase #5	$223.78	6.747%	$238.8784	$238.88	$238.90	$238.90
Purchase #6	$229.57	8.176%	$248.3396	$248.34	$248.35	$248.30
Purchase #7	$94.94	11.214%	$105.5866	$105.59	$105.60	$105.60
7 purchase totals =	$1,242.54		$1,367.1965	$1,367.20	$1,367.25	$1,367.20