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	$50.76	13.487%	$57.606	$57.61	$57.60	$57.60
Purchase #2	$181.58	12.862%	$204.9348	$204.93	$204.95	$204.90
Purchase #3	$112.86	7.198%	$120.9837	$120.98	$121.00	$121.00
Purchase #4	$57.57	3.646%	$59.669	$59.67	$59.65	$59.70
Purchase #5	$174.86	7.836%	$188.562	$188.56	$188.55	$188.60
Purchase #6	$132.50	5.331%	$139.5636	$139.56	$139.55	$139.60
Purchase #7	$78.43	12.271%	$88.0541	$88.05	$88.05	$88.10
7 purchase totals =	$788.56		$859.3732	$859.36	$859.35	$859.50