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	$33.49	7.291%	$35.9318	$35.93	$35.95	$35.90
Purchase #2	$130.86	6.663%	$139.5792	$139.58	$139.60	$139.60
Purchase #3	$148.38	4.624%	$155.2411	$155.24	$155.25	$155.20
Purchase #4	$31.77	10.606%	$35.1395	$35.14	$35.15	$35.10
Purchase #5	$239.59	4.552%	$250.4961	$250.50	$250.50	$250.50
Purchase #6	$89.44	12.493%	$100.6137	$100.61	$100.60	$100.60
Purchase #7	$83.79	3.384%	$86.6255	$86.63	$86.65	$86.60
7 purchase totals =	$757.32		$803.6269	$803.63	$803.70	$803.50