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	$127.50	9.696%	$139.8624	$139.86	$139.85	$139.90
Purchase #2	$94.50	11.732%	$105.5867	$105.59	$105.60	$105.60
Purchase #3	$74.89	7.463%	$80.479	$80.48	$80.50	$80.50
Purchase #4	$44.70	6.547%	$47.6265	$47.63	$47.65	$47.60
Purchase #5	$45.90	4.812%	$48.1087	$48.11	$48.10	$48.10
Purchase #6	$92.88	5.842%	$98.306	$98.31	$98.30	$98.30
Purchase #7	$38.83	11.813%	$43.417	$43.42	$43.40	$43.40
7 purchase totals =	$519.20		$563.3863	$563.40	$563.40	$563.40