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	$38.51	9.803%	$42.2851	$42.29	$42.30	$42.30
Purchase #2	$220.88	4.765%	$231.4049	$231.40	$231.40	$231.40
Purchase #3	$62.49	7.353%	$67.0849	$67.08	$67.10	$67.10
Purchase #4	$75.62	6.163%	$80.2805	$80.28	$80.30	$80.30
Purchase #5	$138.46	9.344%	$151.3977	$151.40	$151.40	$151.40
Purchase #6	$38.37	12.420%	$43.1356	$43.14	$43.15	$43.10
Purchase #7	$109.97	12.133%	$123.3127	$123.31	$123.30	$123.30
7 purchase totals =	$684.30		$738.9014	$738.90	$738.95	$738.90