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	$84.78	6.611%	$90.3848	$90.38	$90.40	$90.40
Purchase #2	$241.92	7.753%	$260.6761	$260.68	$260.70	$260.70
Purchase #3	$135.46	5.624%	$143.0783	$143.08	$143.10	$143.10
Purchase #4	$33.84	4.297%	$35.2941	$35.29	$35.30	$35.30
Purchase #5	$48.44	12.482%	$54.4863	$54.49	$54.50	$54.50
Purchase #6	$40.60	5.190%	$42.7071	$42.71	$42.70	$42.70
Purchase #7	$161.72	11.611%	$180.4973	$180.50	$180.50	$180.50
7 purchase totals =	$746.76		$807.1240	$807.13	$807.20	$807.20