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	$207.98	8.264%	$225.1675	$225.17	$225.15	$225.20
Purchase #2	$118.54	4.488%	$123.8601	$123.86	$123.85	$123.90
Purchase #3	$212.96	12.487%	$239.5523	$239.55	$239.55	$239.60
Purchase #4	$64.96	12.141%	$72.8468	$72.85	$72.85	$72.80
Purchase #5	$119.74	9.697%	$131.3512	$131.35	$131.35	$131.40
Purchase #6	$59.71	11.699%	$66.6955	$66.70	$66.70	$66.70
Purchase #7	$135.51	4.408%	$141.4833	$141.48	$141.50	$141.50
7 purchase totals =	$919.40		$1,000.9567	$1,000.96	$1,000.95	$1,001.10