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	$78.52	13.210%	$88.8925	$88.89	$88.90	$88.90
Purchase #2	$213.84	12.642%	$240.8737	$240.87	$240.85	$240.90
Purchase #3	$93.72	7.671%	$100.9093	$100.91	$100.90	$100.90
Purchase #4	$191.42	9.199%	$209.0287	$209.03	$209.05	$209.00
Purchase #5	$7.36	7.291%	$7.8966	$7.90	$7.90	$7.90
Purchase #6	$181.71	7.712%	$195.7235	$195.72	$195.70	$195.70
Purchase #7	$80.97	11.640%	$90.3949	$90.39	$90.40	$90.40
7 purchase totals =	$847.54		$933.7192	$933.71	$933.70	$933.70