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	$186.54	5.542%	$196.878	$196.88	$196.90	$196.90
Purchase #2	$190.56	7.509%	$204.8692	$204.87	$204.85	$204.90
Purchase #3	$61.72	3.278%	$63.7432	$63.74	$63.75	$63.70
Purchase #4	$124.38	11.336%	$138.4797	$138.48	$138.50	$138.50
Purchase #5	$112.73	10.612%	$124.6929	$124.69	$124.70	$124.70
Purchase #6	$78.74	6.592%	$83.9305	$83.93	$83.95	$83.90
Purchase #7	$178.39	6.751%	$190.4331	$190.43	$190.45	$190.40
7 purchase totals =	$933.06		$1,003.0266	$1,003.02	$1,003.10	$1,003.00