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	$124.93	12.798%	$140.9185	$140.92	$140.90	$140.90
Purchase #2	$85.81	4.748%	$89.8843	$89.88	$89.90	$89.90
Purchase #3	$126.64	11.442%	$141.1301	$141.13	$141.15	$141.10
Purchase #4	$109.64	3.628%	$113.6177	$113.62	$113.60	$113.60
Purchase #5	$245.74	10.406%	$271.3117	$271.31	$271.30	$271.30
Purchase #6	$78.29	9.216%	$85.5052	$85.51	$85.50	$85.50
Purchase #7	$53.47	11.393%	$59.5618	$59.56	$59.55	$59.60
7 purchase totals =	$824.52		$901.9293	$901.93	$901.90	$901.90