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	$217.80	10.601%	$240.889	$240.89	$240.90	$240.90
Purchase #2	$58.50	13.433%	$66.3583	$66.36	$66.35	$66.40
Purchase #3	$154.29	6.492%	$164.3065	$164.31	$164.30	$164.30
Purchase #4	$79.35	12.833%	$89.533	$89.53	$89.55	$89.50
Purchase #5	$124.67	3.230%	$128.6968	$128.70	$128.70	$128.70
Purchase #6	$38.88	4.772%	$40.7354	$40.74	$40.75	$40.70
Purchase #7	$185.59	12.360%	$208.5289	$208.53	$208.55	$208.50
7 purchase totals =	$859.08		$939.0479	$939.06	$939.10	$939.00