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	$183.36	9.104%	$200.0531	$200.05	$200.05	$200.10
Purchase #2	$23.85	13.790%	$27.1389	$27.14	$27.15	$27.10
Purchase #3	$57.29	4.624%	$59.9391	$59.94	$59.95	$59.90
Purchase #4	$231.60	11.811%	$258.9543	$258.95	$258.95	$259.00
Purchase #5	$88.94	13.214%	$100.6925	$100.69	$100.70	$100.70
Purchase #6	$18.90	11.818%	$21.1336	$21.13	$21.15	$21.10
Purchase #7	$163.25	6.791%	$174.3363	$174.34	$174.35	$174.30
7 purchase totals =	$767.19		$842.2478	$842.24	$842.30	$842.20