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	$98.39	13.144%	$111.3224	$111.32	$111.30	$111.30
Purchase #2	$179.36	12.660%	$202.067	$202.07	$202.05	$202.10
Purchase #3	$147.49	7.446%	$158.4721	$158.47	$158.45	$158.50
Purchase #4	$29.39	11.532%	$32.7793	$32.78	$32.80	$32.80
Purchase #5	$87.31	3.497%	$90.3632	$90.36	$90.35	$90.40
Purchase #6	$234.70	10.263%	$258.7873	$258.79	$258.80	$258.80
Purchase #7	$23.57	6.200%	$25.0313	$25.03	$25.05	$25.00
7 purchase totals =	$800.21		$878.8226	$878.82	$878.80	$878.90