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	$128.46	10.832%	$142.3748	$142.37	$142.35	$142.40
Purchase #2	$54.82	4.422%	$57.2441	$57.24	$57.25	$57.20
Purchase #3	$35.65	8.310%	$38.6125	$38.61	$38.60	$38.60
Purchase #4	$32.54	10.615%	$35.9941	$35.99	$36.00	$36.00
Purchase #5	$11.78	6.421%	$12.5364	$12.54	$12.55	$12.50
Purchase #6	$201.78	3.556%	$208.9553	$208.96	$208.95	$209.00
Purchase #7	$150.86	13.496%	$171.2201	$171.22	$171.20	$171.20
7 purchase totals =	$615.89		$666.9373	$666.93	$666.90	$666.90