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	$76.43	9.127%	$83.4058	$83.41	$83.40	$83.40
Purchase #2	$33.44	4.239%	$34.8575	$34.86	$34.85	$34.90
Purchase #3	$182.76	4.231%	$190.4926	$190.49	$190.50	$190.50
Purchase #4	$91.72	7.510%	$98.6082	$98.61	$98.60	$98.60
Purchase #5	$218.77	3.438%	$226.2913	$226.29	$226.30	$226.30
Purchase #6	$22.52	6.410%	$23.9635	$23.96	$23.95	$24.00
Purchase #7	$121.80	7.681%	$131.1555	$131.16	$131.15	$131.20
7 purchase totals =	$747.44		$788.7744	$788.78	$788.75	$788.90