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	$19.36	12.212%	$21.7242	$21.72	$21.70	$21.70
Purchase #2	$201.43	10.674%	$222.9306	$222.93	$222.95	$222.90
Purchase #3	$238.89	3.619%	$247.5354	$247.54	$247.55	$247.50
Purchase #4	$111.33	7.309%	$119.4671	$119.47	$119.45	$119.50
Purchase #5	$194.62	9.571%	$213.2471	$213.25	$213.25	$213.20
Purchase #6	$105.47	6.702%	$112.5386	$112.54	$112.55	$112.50
Purchase #7	$233.31	10.604%	$258.0502	$258.05	$258.05	$258.10
7 purchase totals =	$1,104.41		$1,195.4932	$1,195.50	$1,195.50	$1,195.40