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	$58.98	12.387%	$66.2859	$66.29	$66.30	$66.30
Purchase #2	$62.69	4.577%	$65.5593	$65.56	$65.55	$65.60
Purchase #3	$141.55	4.824%	$148.3784	$148.38	$148.40	$148.40
Purchase #4	$68.36	5.780%	$72.3112	$72.31	$72.30	$72.30
Purchase #5	$146.35	10.118%	$161.1577	$161.16	$161.15	$161.20
Purchase #6	$40.34	7.120%	$43.2122	$43.21	$43.20	$43.20
Purchase #7	$73.51	6.351%	$78.1786	$78.18	$78.20	$78.20
7 purchase totals =	$591.78		$635.0833	$635.09	$635.10	$635.20