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	$234.88	6.628%	$250.4478	$250.45	$250.45	$250.40
Purchase #2	$50.99	5.223%	$53.6532	$53.65	$53.65	$53.70
Purchase #3	$191.59	6.802%	$204.622	$204.62	$204.60	$204.60
Purchase #4	$85.35	6.366%	$90.7834	$90.78	$90.80	$90.80
Purchase #5	$231.89	3.712%	$240.4978	$240.50	$240.50	$240.50
Purchase #6	$119.46	11.746%	$133.4918	$133.49	$133.50	$133.50
Purchase #7	$46.48	8.311%	$50.343	$50.34	$50.35	$50.30
7 purchase totals =	$960.64		$1,023.8390	$1,023.83	$1,023.85	$1,023.80