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	$76.37	5.479%	$80.5543	$80.55	$80.55	$80.60
Purchase #2	$202.28	6.740%	$215.9137	$215.91	$215.90	$215.90
Purchase #3	$90.45	13.523%	$102.6816	$102.68	$102.70	$102.70
Purchase #4	$58.27	10.611%	$64.453	$64.45	$64.45	$64.50
Purchase #5	$135.94	5.622%	$143.5825	$143.58	$143.60	$143.60
Purchase #6	$66.78	9.115%	$72.867	$72.87	$72.85	$72.90
Purchase #7	$239.27	10.562%	$264.5417	$264.54	$264.55	$264.50
7 purchase totals =	$869.36		$944.5938	$944.58	$944.60	$944.70