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	$176.64	6.134%	$187.4751	$187.48	$187.50	$187.50
Purchase #2	$200.66	7.803%	$216.3175	$216.32	$216.30	$216.30
Purchase #3	$215.67	3.250%	$222.6793	$222.68	$222.70	$222.70
Purchase #4	$27.51	10.812%	$30.4844	$30.48	$30.50	$30.50
Purchase #5	$133.26	7.208%	$142.8654	$142.87	$142.85	$142.90
Purchase #6	$121.83	4.532%	$127.3513	$127.35	$127.35	$127.40
Purchase #7	$55.97	12.427%	$62.9254	$62.93	$62.95	$62.90
7 purchase totals =	$931.54		$990.0984	$990.11	$990.15	$990.20