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	$5.46	4.696%	$5.7164	$5.72	$5.70	$5.70
Purchase #2	$71.34	10.529%	$78.8514	$78.85	$78.85	$78.90
Purchase #3	$249.92	12.160%	$280.3103	$280.31	$280.30	$280.30
Purchase #4	$20.46	3.599%	$21.1964	$21.20	$21.20	$21.20
Purchase #5	$159.45	12.342%	$179.1293	$179.13	$179.15	$179.10
Purchase #6	$93.74	8.142%	$101.3723	$101.37	$101.35	$101.40
Purchase #7	$52.97	5.513%	$55.8902	$55.89	$55.90	$55.90
7 purchase totals =	$653.34		$722.4663	$722.47	$722.45	$722.50