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	$37.94	12.129%	$42.5417	$42.54	$42.55	$42.50
Purchase #2	$80.93	11.813%	$90.4903	$90.49	$90.50	$90.50
Purchase #3	$15.97	3.646%	$16.5523	$16.55	$16.55	$16.60
Purchase #4	$220.99	13.241%	$250.2513	$250.25	$250.25	$250.30
Purchase #5	$99.59	12.745%	$112.2827	$112.28	$112.30	$112.30
Purchase #6	$55.85	13.546%	$63.4154	$63.42	$63.40	$63.40
Purchase #7	$49.55	9.805%	$54.4084	$54.41	$54.40	$54.40
7 purchase totals =	$560.82		$629.9421	$629.94	$629.95	$630.00