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	$64.46	12.352%	$72.4221	$72.42	$72.40	$72.40
Purchase #2	$222.70	5.790%	$235.5943	$235.59	$235.60	$235.60
Purchase #3	$89.35	10.706%	$98.9158	$98.92	$98.90	$98.90
Purchase #4	$121.88	7.602%	$131.1453	$131.15	$131.15	$131.10
Purchase #5	$225.48	9.354%	$246.5714	$246.57	$246.55	$246.60
Purchase #6	$147.72	12.388%	$166.0196	$166.02	$166.00	$166.00
Purchase #7	$92.76	13.737%	$105.5024	$105.50	$105.50	$105.50
7 purchase totals =	$964.35		$1,056.1709	$1,056.17	$1,056.10	$1,056.10