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	$178.65	6.624%	$190.4838	$190.48	$190.50	$190.50
Purchase #2	$63.38	7.131%	$67.8996	$67.90	$67.90	$67.90
Purchase #3	$46.90	10.684%	$51.9108	$51.91	$51.90	$51.90
Purchase #4	$148.88	7.677%	$160.3095	$160.31	$160.30	$160.30
Purchase #5	$13.93	4.333%	$14.5336	$14.53	$14.55	$14.50
Purchase #6	$75.29	6.555%	$80.2253	$80.23	$80.25	$80.20
Purchase #7	$11.86	9.361%	$12.9702	$12.97	$12.95	$13.00
7 purchase totals =	$538.89		$578.3328	$578.33	$578.35	$578.30