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	$25.91	10.192%	$28.5507	$28.55	$28.55	$28.60
Purchase #2	$153.41	7.545%	$164.9848	$164.98	$165.00	$165.00
Purchase #3	$79.81	3.844%	$82.8779	$82.88	$82.90	$82.90
Purchase #4	$52.54	11.521%	$58.5931	$58.59	$58.60	$58.60
Purchase #5	$86.94	5.591%	$91.8008	$91.80	$91.80	$91.80
Purchase #6	$27.79	11.675%	$31.0345	$31.03	$31.05	$31.00
Purchase #7	$212.71	4.523%	$222.3309	$222.33	$222.35	$222.30
7 purchase totals =	$639.11		$680.1727	$680.16	$680.25	$680.20