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	$238.52	9.798%	$261.8902	$261.89	$261.90	$261.90
Purchase #2	$126.79	6.461%	$134.9819	$134.98	$135.00	$135.00
Purchase #3	$133.93	12.120%	$150.1623	$150.16	$150.15	$150.20
Purchase #4	$76.28	9.577%	$83.5853	$83.59	$83.60	$83.60
Purchase #5	$164.72	10.232%	$181.5742	$181.57	$181.55	$181.60
Purchase #6	$221.92	10.817%	$245.9251	$245.93	$245.95	$245.90
Purchase #7	$188.47	4.117%	$196.2293	$196.23	$196.25	$196.20
7 purchase totals =	$1,150.63		$1,254.3483	$1,254.35	$1,254.40	$1,254.40