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	$245.87	10.447%	$271.556	$271.56	$271.55	$271.60
Purchase #2	$53.91	3.358%	$55.7203	$55.72	$55.70	$55.70
Purchase #3	$143.73	9.795%	$157.8084	$157.81	$157.80	$157.80
Purchase #4	$116.51	12.567%	$131.1518	$131.15	$131.15	$131.20
Purchase #5	$217.90	8.227%	$235.8266	$235.83	$235.85	$235.80
Purchase #6	$99.76	4.225%	$103.9749	$103.97	$103.95	$104.00
Purchase #7	$139.54	3.137%	$143.9174	$143.92	$143.90	$143.90
7 purchase totals =	$1,017.22		$1,099.9554	$1,099.96	$1,099.90	$1,100.00