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	$186.50	6.600%	$198.809	$198.81	$198.80	$198.80
Purchase #2	$32.81	4.809%	$34.3878	$34.39	$34.40	$34.40
Purchase #3	$161.50	9.390%	$176.6649	$176.66	$176.65	$176.70
Purchase #4	$76.94	7.123%	$82.4204	$82.42	$82.40	$82.40
Purchase #5	$82.31	10.374%	$90.8488	$90.85	$90.85	$90.80
Purchase #6	$128.70	5.310%	$135.534	$135.53	$135.55	$135.50
Purchase #7	$177.77	10.751%	$196.8821	$196.88	$196.90	$196.90
7 purchase totals =	$846.53		$915.5470	$915.54	$915.55	$915.50