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	$132.41	5.659%	$139.9031	$139.90	$139.90	$139.90
Purchase #2	$159.70	12.626%	$179.8637	$179.86	$179.85	$179.90
Purchase #3	$199.71	13.122%	$225.9159	$225.92	$225.90	$225.90
Purchase #4	$112.89	9.579%	$123.7037	$123.70	$123.70	$123.70
Purchase #5	$32.75	6.766%	$34.9659	$34.97	$34.95	$35.00
Purchase #6	$89.99	13.629%	$102.2547	$102.25	$102.25	$102.30
Purchase #7	$196.25	11.346%	$218.5165	$218.52	$218.50	$218.50
7 purchase totals =	$923.70		$1,025.1235	$1,025.12	$1,025.05	$1,025.20