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	$35.47	10.871%	$39.3259	$39.33	$39.35	$39.30
Purchase #2	$239.78	4.131%	$249.6853	$249.69	$249.70	$249.70
Purchase #3	$107.77	10.326%	$118.8983	$118.90	$118.90	$118.90
Purchase #4	$89.58	12.626%	$100.8904	$100.89	$100.90	$100.90
Purchase #5	$57.92	13.268%	$65.6048	$65.60	$65.60	$65.60
Purchase #6	$160.40	4.289%	$167.2796	$167.28	$167.30	$167.30
Purchase #7	$112.82	10.481%	$124.6447	$124.64	$124.65	$124.60
7 purchase totals =	$803.74		$866.3290	$866.33	$866.40	$866.30