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	$81.34	6.212%	$86.3928	$86.39	$86.40	$86.40
Purchase #2	$169.38	11.210%	$188.3675	$188.37	$188.35	$188.40
Purchase #3	$96.59	3.552%	$100.0209	$100.02	$100.00	$100.00
Purchase #4	$201.31	9.605%	$220.6458	$220.65	$220.65	$220.60
Purchase #5	$83.49	8.661%	$90.7211	$90.72	$90.70	$90.70
Purchase #6	$213.88	10.595%	$236.5406	$236.54	$236.55	$236.50
Purchase #7	$203.69	3.168%	$210.1429	$210.14	$210.15	$210.10
7 purchase totals =	$1,049.68		$1,132.8316	$1,132.83	$1,132.80	$1,132.70