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	$47.58	12.227%	$53.3976	$53.40	$53.40	$53.40
Purchase #2	$97.88	4.521%	$102.3052	$102.31	$102.30	$102.30
Purchase #3	$79.66	3.628%	$82.5501	$82.55	$82.55	$82.60
Purchase #4	$73.55	12.504%	$82.7467	$82.75	$82.75	$82.70
Purchase #5	$72.83	10.485%	$80.4662	$80.47	$80.45	$80.50
Purchase #6	$118.78	13.392%	$134.687	$134.69	$134.70	$134.70
Purchase #7	$115.58	3.648%	$119.7964	$119.80	$119.80	$119.80
7 purchase totals =	$605.86		$655.9492	$655.97	$655.95	$656.00