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	$156.26	9.653%	$171.3438	$171.34	$171.35	$171.30
Purchase #2	$132.50	12.353%	$148.8677	$148.87	$148.85	$148.90
Purchase #3	$179.86	11.377%	$200.3227	$200.32	$200.30	$200.30
Purchase #4	$120.87	13.715%	$137.4473	$137.45	$137.45	$137.40
Purchase #5	$248.27	10.473%	$274.2713	$274.27	$274.25	$274.30
Purchase #6	$38.64	4.610%	$40.4213	$40.42	$40.40	$40.40
Purchase #7	$102.98	10.672%	$113.97	$113.97	$113.95	$114.00
7 purchase totals =	$979.38		$1,086.6441	$1,086.64	$1,086.55	$1,086.60