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	$72.31	11.498%	$80.6242	$80.62	$80.60	$80.60
Purchase #2	$71.51	9.833%	$78.5416	$78.54	$78.55	$78.50
Purchase #3	$231.62	9.234%	$253.0078	$253.01	$253.00	$253.00
Purchase #4	$9.34	13.265%	$10.579	$10.58	$10.60	$10.60
Purchase #5	$40.90	8.434%	$44.3495	$44.35	$44.35	$44.30
Purchase #6	$213.60	5.458%	$225.2583	$225.26	$225.25	$225.30
Purchase #7	$74.56	4.802%	$78.1404	$78.14	$78.15	$78.10
7 purchase totals =	$713.84		$770.5008	$770.50	$770.50	$770.40