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	$32.67	5.137%	$34.3483	$34.35	$34.35	$34.30
Purchase #2	$116.71	5.617%	$123.2656	$123.27	$123.25	$123.30
Purchase #3	$187.71	3.549%	$194.3718	$194.37	$194.35	$194.40
Purchase #4	$72.57	8.230%	$78.5425	$78.54	$78.55	$78.50
Purchase #5	$109.49	9.442%	$119.828	$119.83	$119.85	$119.80
Purchase #6	$5.92	13.577%	$6.7238	$6.72	$6.70	$6.70
Purchase #7	$228.73	7.433%	$245.7315	$245.73	$245.75	$245.70
7 purchase totals =	$753.80		$802.8115	$802.81	$802.80	$802.70