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	$99.74	9.559%	$109.2741	$109.27	$109.25	$109.30
Purchase #2	$37.59	6.331%	$39.9698	$39.97	$39.95	$40.00
Purchase #3	$127.68	12.846%	$144.0818	$144.08	$144.10	$144.10
Purchase #4	$24.99	7.593%	$26.8875	$26.89	$26.90	$26.90
Purchase #5	$228.46	7.772%	$246.2159	$246.22	$246.20	$246.20
Purchase #6	$178.31	12.696%	$200.9482	$200.95	$200.95	$200.90
Purchase #7	$98.72	12.697%	$111.2545	$111.25	$111.25	$111.30
7 purchase totals =	$795.49		$878.6318	$878.63	$878.60	$878.70