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	$6.62	12.744%	$7.4637	$7.46	$7.45	$7.50
Purchase #2	$135.45	7.499%	$145.6074	$145.61	$145.60	$145.60
Purchase #3	$137.27	4.682%	$143.697	$143.70	$143.70	$143.70
Purchase #4	$166.85	3.296%	$172.3494	$172.35	$172.35	$172.30
Purchase #5	$159.43	5.606%	$168.3676	$168.37	$168.35	$168.40
Purchase #6	$81.58	4.458%	$85.2168	$85.22	$85.20	$85.20
Purchase #7	$191.34	8.126%	$206.8883	$206.89	$206.90	$206.90
7 purchase totals =	$878.54		$929.5902	$929.60	$929.55	$929.60