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	$231.35	8.651%	$251.3641	$251.36	$251.35	$251.40
Purchase #2	$103.41	13.627%	$117.5017	$117.50	$117.50	$117.50
Purchase #3	$57.34	3.816%	$59.5281	$59.53	$59.55	$59.50
Purchase #4	$61.86	8.874%	$67.3495	$67.35	$67.35	$67.30
Purchase #5	$218.31	5.157%	$229.5682	$229.57	$229.55	$229.60
Purchase #6	$105.85	12.154%	$118.715	$118.72	$118.70	$118.70
Purchase #7	$71.32	4.486%	$74.5194	$74.52	$74.50	$74.50
7 purchase totals =	$849.44		$918.5460	$918.55	$918.50	$918.50