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	$100.71	3.182%	$103.9146	$103.91	$103.90	$103.90
Purchase #2	$185.84	3.291%	$191.956	$191.96	$191.95	$192.00
Purchase #3	$135.47	4.369%	$141.3887	$141.39	$141.40	$141.40
Purchase #4	$102.29	3.250%	$105.6144	$105.61	$105.60	$105.60
Purchase #5	$10.82	6.474%	$11.5205	$11.52	$11.50	$11.50
Purchase #6	$136.68	3.338%	$141.2424	$141.24	$141.25	$141.20
Purchase #7	$41.51	5.360%	$43.7349	$43.73	$43.75	$43.70
7 purchase totals =	$713.32		$739.3715	$739.36	$739.35	$739.30