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	$30.56	3.192%	$31.5355	$31.54	$31.55	$31.50
Purchase #2	$117.72	4.612%	$123.1492	$123.15	$123.15	$123.10
Purchase #3	$149.58	6.761%	$159.6931	$159.69	$159.70	$159.70
Purchase #4	$167.89	12.838%	$189.4437	$189.44	$189.45	$189.40
Purchase #5	$100.67	6.301%	$107.0132	$107.01	$107.00	$107.00
Purchase #6	$146.34	11.681%	$163.434	$163.43	$163.45	$163.40
Purchase #7	$79.83	12.254%	$89.6124	$89.61	$89.60	$89.60
7 purchase totals =	$792.59		$863.8811	$863.87	$863.90	$863.70