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	$188.83	12.524%	$212.4791	$212.48	$212.50	$212.50
Purchase #2	$114.80	4.190%	$119.6101	$119.61	$119.60	$119.60
Purchase #3	$20.92	3.111%	$21.5708	$21.57	$21.55	$21.60
Purchase #4	$76.71	5.455%	$80.8945	$80.89	$80.90	$80.90
Purchase #5	$167.68	6.315%	$178.269	$178.27	$178.25	$178.30
Purchase #6	$27.98	5.467%	$29.5097	$29.51	$29.50	$29.50
Purchase #7	$249.38	7.249%	$267.4576	$267.46	$267.45	$267.50
7 purchase totals =	$846.30		$909.7908	$909.79	$909.75	$909.90