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	$72.80	13.411%	$82.5632	$82.56	$82.55	$82.60
Purchase #2	$30.70	4.567%	$32.1021	$32.10	$32.10	$32.10
Purchase #3	$221.45	7.398%	$237.8329	$237.83	$237.85	$237.80
Purchase #4	$68.83	13.663%	$78.2342	$78.23	$78.25	$78.20
Purchase #5	$77.79	11.593%	$86.8082	$86.81	$86.80	$86.80
Purchase #6	$77.47	10.291%	$85.4424	$85.44	$85.45	$85.40
Purchase #7	$45.72	3.547%	$47.3417	$47.34	$47.35	$47.30
7 purchase totals =	$594.76		$650.3247	$650.31	$650.35	$650.20