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	$6.71	13.390%	$7.6085	$7.61	$7.60	$7.60
Purchase #2	$75.53	8.773%	$82.1562	$82.16	$82.15	$82.20
Purchase #3	$237.96	6.650%	$253.7843	$253.78	$253.80	$253.80
Purchase #4	$203.74	9.209%	$222.5024	$222.50	$222.50	$222.50
Purchase #5	$108.38	3.840%	$112.5418	$112.54	$112.55	$112.50
Purchase #6	$141.85	5.144%	$149.1468	$149.15	$149.15	$149.10
Purchase #7	$200.64	9.181%	$219.0608	$219.06	$219.05	$219.10
7 purchase totals =	$974.81		$1,046.8008	$1,046.80	$1,046.80	$1,046.80