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	$67.96	12.558%	$76.4944	$76.49	$76.50	$76.50
Purchase #2	$217.50	6.359%	$231.3308	$231.33	$231.35	$231.30
Purchase #3	$155.34	11.221%	$172.7707	$172.77	$172.75	$172.80
Purchase #4	$113.89	12.610%	$128.2515	$128.25	$128.25	$128.30
Purchase #5	$30.73	11.718%	$34.3309	$34.33	$34.35	$34.30
Purchase #6	$138.61	13.137%	$156.8192	$156.82	$156.80	$156.80
Purchase #7	$103.45	9.739%	$113.525	$113.53	$113.55	$113.50
7 purchase totals =	$827.48		$913.5225	$913.52	$913.55	$913.50