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	$138.86	8.132%	$150.1521	$150.15	$150.15	$150.20
Purchase #2	$185.29	9.538%	$202.963	$202.96	$202.95	$203.00
Purchase #3	$151.78	5.835%	$160.6364	$160.64	$160.65	$160.60
Purchase #4	$241.30	13.388%	$273.6052	$273.61	$273.60	$273.60
Purchase #5	$63.86	3.200%	$65.9035	$65.90	$65.90	$65.90
Purchase #6	$100.59	8.843%	$109.4852	$109.49	$109.50	$109.50
Purchase #7	$241.43	7.469%	$259.4624	$259.46	$259.45	$259.50
7 purchase totals =	$1,123.11		$1,222.2078	$1,222.21	$1,222.20	$1,222.30