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	$82.98	5.208%	$87.3016	$87.30	$87.30	$87.30
Purchase #2	$194.73	10.747%	$215.6576	$215.66	$215.65	$215.70
Purchase #3	$82.71	6.408%	$88.0101	$88.01	$88.00	$88.00
Purchase #4	$94.94	7.538%	$102.0966	$102.10	$102.10	$102.10
Purchase #5	$67.48	7.122%	$72.2859	$72.29	$72.30	$72.30
Purchase #6	$92.81	13.551%	$105.3867	$105.39	$105.40	$105.40
Purchase #7	$150.72	13.865%	$171.6173	$171.62	$171.60	$171.60
7 purchase totals =	$766.37		$842.3558	$842.37	$842.35	$842.40