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	$13.31	4.780%	$13.9462	$13.95	$13.95	$13.90
Purchase #2	$141.96	5.679%	$150.0219	$150.02	$150.00	$150.00
Purchase #3	$82.38	8.453%	$89.3436	$89.34	$89.35	$89.30
Purchase #4	$60.82	8.386%	$65.9204	$65.92	$65.90	$65.90
Purchase #5	$34.71	7.513%	$37.3178	$37.32	$37.30	$37.30
Purchase #6	$135.94	10.740%	$150.54	$150.54	$150.55	$150.50
Purchase #7	$112.67	9.170%	$123.0018	$123.00	$123.00	$123.00
7 purchase totals =	$581.79		$630.0917	$630.09	$630.05	$629.90