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	$227.90	6.370%	$242.4172	$242.42	$242.40	$242.40
Purchase #2	$87.56	7.771%	$94.3643	$94.36	$94.35	$94.40
Purchase #3	$136.35	3.381%	$140.96	$140.96	$140.95	$141.00
Purchase #4	$142.40	8.873%	$155.0352	$155.04	$155.05	$155.00
Purchase #5	$85.25	6.380%	$90.689	$90.69	$90.70	$90.70
Purchase #6	$16.75	10.247%	$18.4664	$18.47	$18.45	$18.50
Purchase #7	$103.55	7.582%	$111.4012	$111.40	$111.40	$111.40
7 purchase totals =	$799.76		$853.3333	$853.34	$853.30	$853.40