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	$241.38	10.146%	$265.8704	$265.87	$265.85	$265.90
Purchase #2	$215.70	4.288%	$224.9492	$224.95	$224.95	$224.90
Purchase #3	$88.87	12.866%	$100.304	$100.30	$100.30	$100.30
Purchase #4	$76.64	7.178%	$82.1412	$82.14	$82.15	$82.10
Purchase #5	$46.58	7.181%	$49.9249	$49.92	$49.90	$49.90
Purchase #6	$31.44	11.364%	$35.0128	$35.01	$35.00	$35.00
Purchase #7	$38.47	6.347%	$40.9117	$40.91	$40.90	$40.90
7 purchase totals =	$739.08		$799.1142	$799.10	$799.05	$799.00