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	$150.84	10.841%	$167.1926	$167.19	$167.20	$167.20
Purchase #2	$60.76	9.440%	$66.4957	$66.50	$66.50	$66.50
Purchase #3	$27.31	12.470%	$30.7156	$30.72	$30.70	$30.70
Purchase #4	$167.79	9.724%	$184.1059	$184.11	$184.10	$184.10
Purchase #5	$64.57	9.750%	$70.8656	$70.87	$70.85	$70.90
Purchase #6	$82.33	12.864%	$92.9209	$92.92	$92.90	$92.90
Purchase #7	$52.83	12.437%	$59.4005	$59.40	$59.40	$59.40
7 purchase totals =	$606.43		$671.6968	$671.71	$671.65	$671.70