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	$94.26	3.855%	$97.8937	$97.89	$97.90	$97.90
Purchase #2	$60.31	3.614%	$62.4896	$62.49	$62.50	$62.50
Purchase #3	$75.51	6.170%	$80.169	$80.17	$80.15	$80.20
Purchase #4	$191.69	13.387%	$217.3515	$217.35	$217.35	$217.40
Purchase #5	$96.95	5.779%	$102.5527	$102.55	$102.55	$102.60
Purchase #6	$126.82	13.113%	$143.4499	$143.45	$143.45	$143.40
Purchase #7	$35.98	9.828%	$39.5161	$39.52	$39.50	$39.50
7 purchase totals =	$681.52		$743.4225	$743.42	$743.40	$743.50