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	$109.26	9.584%	$119.7315	$119.73	$119.75	$119.70
Purchase #2	$144.98	5.439%	$152.8655	$152.87	$152.85	$152.90
Purchase #3	$7.86	12.212%	$8.8199	$8.82	$8.80	$8.80
Purchase #4	$40.89	10.352%	$45.1229	$45.12	$45.10	$45.10
Purchase #5	$101.73	7.745%	$109.609	$109.61	$109.60	$109.60
Purchase #6	$129.90	6.628%	$138.5098	$138.51	$138.50	$138.50
Purchase #7	$131.93	4.131%	$137.38	$137.38	$137.40	$137.40
7 purchase totals =	$666.55		$712.0386	$712.04	$712.00	$712.00