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	$12.46	10.404%	$13.7563	$13.76	$13.75	$13.80
Purchase #2	$211.54	6.652%	$225.6116	$225.61	$225.60	$225.60
Purchase #3	$89.66	12.843%	$101.175	$101.18	$101.20	$101.20
Purchase #4	$101.73	5.520%	$107.3455	$107.35	$107.35	$107.30
Purchase #5	$94.71	9.334%	$103.5502	$103.55	$103.55	$103.60
Purchase #6	$34.42	10.170%	$37.9205	$37.92	$37.90	$37.90
Purchase #7	$88.30	11.514%	$98.4669	$98.47	$98.45	$98.50
7 purchase totals =	$632.82		$687.8260	$687.84	$687.80	$687.90