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	$137.60	9.303%	$150.4009	$150.40	$150.40	$150.40
Purchase #2	$231.66	12.141%	$259.7858	$259.79	$259.80	$259.80
Purchase #3	$101.88	7.755%	$109.7808	$109.78	$109.80	$109.80
Purchase #4	$88.43	13.782%	$100.6174	$100.62	$100.60	$100.60
Purchase #5	$92.71	13.123%	$104.8763	$104.88	$104.90	$104.90
Purchase #6	$40.87	5.531%	$43.1305	$43.13	$43.15	$43.10
Purchase #7	$193.34	7.692%	$208.2117	$208.21	$208.20	$208.20
7 purchase totals =	$886.49		$976.8034	$976.81	$976.85	$976.80