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	$48.31	10.267%	$53.27	$53.27	$53.25	$53.30
Purchase #2	$215.54	12.316%	$242.0859	$242.09	$242.10	$242.10
Purchase #3	$222.34	12.259%	$249.5967	$249.60	$249.60	$249.60
Purchase #4	$208.38	6.194%	$221.2871	$221.29	$221.30	$221.30
Purchase #5	$171.49	8.350%	$185.8094	$185.81	$185.80	$185.80
Purchase #6	$227.25	3.360%	$234.8856	$234.89	$234.90	$234.90
Purchase #7	$147.42	6.214%	$156.5807	$156.58	$156.60	$156.60
7 purchase totals =	$1,240.73		$1,343.5154	$1,343.53	$1,343.55	$1,343.60