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	$50.53	9.646%	$55.4041	$55.40	$55.40	$55.40
Purchase #2	$250.49	12.699%	$282.2997	$282.30	$282.30	$282.30
Purchase #3	$236.45	8.200%	$255.8389	$255.84	$255.85	$255.80
Purchase #4	$154.50	4.524%	$161.4896	$161.49	$161.50	$161.50
Purchase #5	$234.56	5.361%	$247.1348	$247.13	$247.15	$247.10
Purchase #6	$96.57	12.800%	$108.931	$108.93	$108.95	$108.90
Purchase #7	$33.46	4.272%	$34.8894	$34.89	$34.90	$34.90
7 purchase totals =	$1,056.56		$1,145.9875	$1,145.98	$1,146.05	$1,145.90