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	$221.39	12.840%	$249.8165	$249.82	$249.80	$249.80
Purchase #2	$241.44	3.764%	$250.5278	$250.53	$250.55	$250.50
Purchase #3	$164.64	8.585%	$178.7743	$178.77	$178.75	$178.80
Purchase #4	$59.68	11.542%	$66.5683	$66.57	$66.55	$66.60
Purchase #5	$36.77	5.310%	$38.7225	$38.72	$38.70	$38.70
Purchase #6	$62.98	3.226%	$65.0117	$65.01	$65.00	$65.00
Purchase #7	$217.83	10.662%	$241.055	$241.06	$241.05	$241.10
7 purchase totals =	$1,004.73		$1,090.4761	$1,090.48	$1,090.40	$1,090.50