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	$248.73	12.338%	$279.4183	$279.42	$279.40	$279.40
Purchase #2	$27.67	6.315%	$29.4174	$29.42	$29.40	$29.40
Purchase #3	$227.33	6.282%	$241.6109	$241.61	$241.60	$241.60
Purchase #4	$36.51	4.573%	$38.1796	$38.18	$38.20	$38.20
Purchase #5	$35.89	4.623%	$37.5492	$37.55	$37.55	$37.50
Purchase #6	$248.88	8.618%	$270.3285	$270.33	$270.35	$270.30
Purchase #7	$11.54	8.227%	$12.4894	$12.49	$12.50	$12.50
7 purchase totals =	$836.55		$908.9933	$909.00	$909.00	$908.90