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	$146.85	6.393%	$156.2381	$156.24	$156.25	$156.20
Purchase #2	$74.80	9.582%	$81.9673	$81.97	$81.95	$82.00
Purchase #3	$141.52	4.164%	$147.4129	$147.41	$147.40	$147.40
Purchase #4	$112.51	10.161%	$123.9421	$123.94	$123.95	$123.90
Purchase #5	$82.59	4.296%	$86.1381	$86.14	$86.15	$86.10
Purchase #6	$199.66	11.640%	$222.9004	$222.90	$222.90	$222.90
Purchase #7	$134.35	5.297%	$141.4665	$141.47	$141.45	$141.50
7 purchase totals =	$892.28		$960.0654	$960.07	$960.05	$960.00