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	$110.55	8.173%	$119.5853	$119.59	$119.60	$119.60
Purchase #2	$159.94	7.581%	$172.0651	$172.07	$172.05	$172.10
Purchase #3	$34.83	10.575%	$38.5133	$38.51	$38.50	$38.50
Purchase #4	$51.36	12.168%	$57.6095	$57.61	$57.60	$57.60
Purchase #5	$10.51	6.747%	$11.2191	$11.22	$11.20	$11.20
Purchase #6	$45.83	12.484%	$51.5514	$51.55	$51.55	$51.60
Purchase #7	$246.98	10.657%	$273.3007	$273.30	$273.30	$273.30
7 purchase totals =	$660.00		$723.8444	$723.85	$723.80	$723.90