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	$179.39	10.862%	$198.8753	$198.88	$198.90	$198.90
Purchase #2	$208.53	12.265%	$234.1062	$234.11	$234.10	$234.10
Purchase #3	$86.47	7.365%	$92.8385	$92.84	$92.85	$92.80
Purchase #4	$39.67	11.672%	$44.3003	$44.30	$44.30	$44.30
Purchase #5	$36.27	3.206%	$37.4328	$37.43	$37.45	$37.40
Purchase #6	$96.69	13.228%	$109.4802	$109.48	$109.50	$109.50
Purchase #7	$19.41	10.779%	$21.5022	$21.50	$21.50	$21.50
7 purchase totals =	$666.43		$738.5355	$738.54	$738.60	$738.50