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	$79.44	12.389%	$89.2818	$89.28	$89.30	$89.30
Purchase #2	$130.77	13.330%	$148.2016	$148.20	$148.20	$148.20
Purchase #3	$160.49	3.677%	$166.3912	$166.39	$166.40	$166.40
Purchase #4	$40.39	11.254%	$44.9355	$44.94	$44.95	$44.90
Purchase #5	$156.71	9.470%	$171.5504	$171.55	$171.55	$171.60
Purchase #6	$248.89	3.102%	$256.6106	$256.61	$256.60	$256.60
Purchase #7	$72.69	10.731%	$80.4904	$80.49	$80.50	$80.50
7 purchase totals =	$889.38		$957.4615	$957.46	$957.50	$957.50