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	$189.75	9.253%	$207.3076	$207.31	$207.30	$207.30
Purchase #2	$55.32	7.620%	$59.5354	$59.54	$59.55	$59.50
Purchase #3	$58.51	11.871%	$65.4557	$65.46	$65.45	$65.50
Purchase #4	$203.49	4.787%	$213.2311	$213.23	$213.25	$213.20
Purchase #5	$53.88	5.388%	$56.7831	$56.78	$56.80	$56.80
Purchase #6	$211.40	10.665%	$233.9458	$233.95	$233.95	$233.90
Purchase #7	$87.47	12.748%	$98.6207	$98.62	$98.60	$98.60
7 purchase totals =	$859.82		$934.8794	$934.89	$934.90	$934.80