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	$168.33	12.488%	$189.3511	$189.35	$189.35	$189.40
Purchase #2	$95.80	4.265%	$99.8859	$99.89	$99.90	$99.90
Purchase #3	$138.94	12.200%	$155.8907	$155.89	$155.90	$155.90
Purchase #4	$40.72	5.671%	$43.0292	$43.03	$43.05	$43.00
Purchase #5	$238.26	4.766%	$249.6155	$249.62	$249.60	$249.60
Purchase #6	$127.69	6.520%	$136.0154	$136.02	$136.00	$136.00
Purchase #7	$55.26	7.754%	$59.5449	$59.54	$59.55	$59.50
7 purchase totals =	$865.00		$933.3327	$933.34	$933.35	$933.30