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	$245.85	10.198%	$270.9218	$270.92	$270.90	$270.90
Purchase #2	$209.87	6.709%	$223.9502	$223.95	$223.95	$224.00
Purchase #3	$163.42	3.404%	$168.9828	$168.98	$169.00	$169.00
Purchase #4	$44.70	12.575%	$50.321	$50.32	$50.30	$50.30
Purchase #5	$77.53	3.693%	$80.3932	$80.39	$80.40	$80.40
Purchase #6	$228.78	5.695%	$241.809	$241.81	$241.80	$241.80
Purchase #7	$207.48	5.770%	$219.4516	$219.45	$219.45	$219.50
7 purchase totals =	$1,177.63		$1,255.8296	$1,255.82	$1,255.80	$1,255.90