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	$226.83	3.526%	$234.828	$234.83	$234.85	$234.80
Purchase #2	$213.29	13.847%	$242.8243	$242.82	$242.80	$242.80
Purchase #3	$41.38	5.571%	$43.6853	$43.69	$43.70	$43.70
Purchase #4	$215.93	6.299%	$229.5314	$229.53	$229.55	$229.50
Purchase #5	$129.93	7.262%	$139.3655	$139.37	$139.35	$139.40
Purchase #6	$8.32	6.611%	$8.87	$8.87	$8.85	$8.90
Purchase #7	$54.76	12.109%	$61.3909	$61.39	$61.40	$61.40
7 purchase totals =	$890.44		$960.4954	$960.50	$960.50	$960.50