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	$247.61	3.175%	$255.4716	$255.47	$255.45	$255.50
Purchase #2	$35.25	13.590%	$40.0405	$40.04	$40.05	$40.00
Purchase #3	$214.43	12.372%	$240.9593	$240.96	$240.95	$241.00
Purchase #4	$123.37	4.612%	$129.0598	$129.06	$129.05	$129.10
Purchase #5	$89.92	13.446%	$102.0106	$102.01	$102.00	$102.00
Purchase #6	$225.94	8.238%	$244.5529	$244.55	$244.55	$244.60
Purchase #7	$76.36	7.487%	$82.0771	$82.08	$82.10	$82.10
7 purchase totals =	$1,012.88		$1,094.1718	$1,094.17	$1,094.15	$1,094.30