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	$242.69	5.450%	$255.9166	$255.92	$255.90	$255.90
Purchase #2	$37.61	13.119%	$42.5441	$42.54	$42.55	$42.50
Purchase #3	$38.47	3.720%	$39.9011	$39.90	$39.90	$39.90
Purchase #4	$216.38	8.338%	$234.4218	$234.42	$234.40	$234.40
Purchase #5	$194.72	4.216%	$202.9294	$202.93	$202.95	$202.90
Purchase #6	$5.37	4.168%	$5.5938	$5.59	$5.60	$5.60
Purchase #7	$73.66	3.601%	$76.3125	$76.31	$76.30	$76.30
7 purchase totals =	$808.90		$857.6193	$857.61	$857.60	$857.50