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	$79.66	13.399%	$90.3336	$90.33	$90.35	$90.30
Purchase #2	$173.90	7.868%	$187.5825	$187.58	$187.60	$187.60
Purchase #3	$145.53	12.346%	$163.4971	$163.50	$163.50	$163.50
Purchase #4	$80.28	7.219%	$86.0754	$86.08	$86.10	$86.10
Purchase #5	$50.37	5.864%	$53.3237	$53.32	$53.30	$53.30
Purchase #6	$223.92	3.410%	$231.5557	$231.56	$231.55	$231.60
Purchase #7	$187.78	5.504%	$198.1154	$198.12	$198.10	$198.10
7 purchase totals =	$941.44		$1,010.4834	$1,010.49	$1,010.50	$1,010.50