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	$72.32	8.470%	$78.4455	$78.45	$78.45	$78.40
Purchase #2	$94.88	6.737%	$101.2721	$101.27	$101.25	$101.30
Purchase #3	$220.63	12.822%	$248.9192	$248.92	$248.90	$248.90
Purchase #4	$32.69	3.608%	$33.8695	$33.87	$33.85	$33.90
Purchase #5	$86.30	4.602%	$90.2715	$90.27	$90.25	$90.30
Purchase #6	$190.37	6.850%	$203.4103	$203.41	$203.40	$203.40
Purchase #7	$104.45	3.128%	$107.7172	$107.72	$107.70	$107.70
7 purchase totals =	$801.64		$863.9053	$863.91	$863.80	$863.90