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	$143.79	13.604%	$163.3512	$163.35	$163.35	$163.40
Purchase #2	$78.31	9.534%	$85.7761	$85.78	$85.80	$85.80
Purchase #3	$50.93	8.338%	$55.1765	$55.18	$55.20	$55.20
Purchase #4	$99.61	12.669%	$112.2296	$112.23	$112.25	$112.20
Purchase #5	$142.71	6.831%	$152.4585	$152.46	$152.45	$152.50
Purchase #6	$160.82	11.299%	$178.9911	$178.99	$179.00	$179.00
Purchase #7	$39.25	5.793%	$41.5238	$41.52	$41.50	$41.50
7 purchase totals =	$715.42		$789.5068	$789.51	$789.55	$789.60