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	$166.39	7.249%	$178.4516	$178.45	$178.45	$178.50
Purchase #2	$94.31	4.368%	$98.4295	$98.43	$98.45	$98.40
Purchase #3	$168.34	5.514%	$177.6223	$177.62	$177.60	$177.60
Purchase #4	$54.57	8.135%	$59.0093	$59.01	$59.00	$59.00
Purchase #5	$106.90	12.266%	$120.0124	$120.01	$120.00	$120.00
Purchase #6	$241.38	3.455%	$249.7197	$249.72	$249.70	$249.70
Purchase #7	$82.85	7.703%	$89.2319	$89.23	$89.25	$89.20
7 purchase totals =	$914.74		$972.4767	$972.47	$972.45	$972.40