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	$33.59	13.168%	$38.0131	$38.01	$38.00	$38.00
Purchase #2	$208.65	6.139%	$221.459	$221.46	$221.45	$221.50
Purchase #3	$241.82	3.369%	$249.9669	$249.97	$249.95	$250.00
Purchase #4	$63.46	12.537%	$71.416	$71.42	$71.40	$71.40
Purchase #5	$131.42	9.290%	$143.6289	$143.63	$143.65	$143.60
Purchase #6	$112.84	5.350%	$118.8769	$118.88	$118.90	$118.90
Purchase #7	$155.48	12.838%	$175.4405	$175.44	$175.45	$175.40
7 purchase totals =	$947.26		$1,018.8013	$1,018.81	$1,018.80	$1,018.80