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	$136.66	4.380%	$142.6457	$142.65	$142.65	$142.60
Purchase #2	$77.52	9.646%	$84.9976	$85.00	$85.00	$85.00
Purchase #3	$9.47	11.154%	$10.5263	$10.53	$10.55	$10.50
Purchase #4	$129.33	11.301%	$143.9456	$143.95	$143.95	$143.90
Purchase #5	$90.32	11.247%	$100.4783	$100.48	$100.50	$100.50
Purchase #6	$163.41	9.165%	$178.3865	$178.39	$178.40	$178.40
Purchase #7	$191.56	3.684%	$198.6171	$198.62	$198.60	$198.60
7 purchase totals =	$798.27		$859.5971	$859.62	$859.65	$859.50