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	$93.80	10.488%	$103.6377	$103.64	$103.65	$103.60
Purchase #2	$82.38	9.603%	$90.291	$90.29	$90.30	$90.30
Purchase #3	$177.56	10.583%	$196.3512	$196.35	$196.35	$196.40
Purchase #4	$147.73	6.794%	$157.7668	$157.77	$157.75	$157.80
Purchase #5	$47.82	5.694%	$50.5429	$50.54	$50.55	$50.50
Purchase #6	$57.61	10.746%	$63.8008	$63.80	$63.80	$63.80
Purchase #7	$148.64	5.354%	$156.5982	$156.60	$156.60	$156.60
7 purchase totals =	$755.54		$818.9886	$818.99	$819.00	$819.00