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	$84.85	5.693%	$89.6805	$89.68	$89.70	$89.70
Purchase #2	$218.87	12.200%	$245.5721	$245.57	$245.55	$245.60
Purchase #3	$190.84	7.257%	$204.6893	$204.69	$204.70	$204.70
Purchase #4	$176.38	7.730%	$190.0142	$190.01	$190.00	$190.00
Purchase #5	$33.27	9.665%	$36.4855	$36.49	$36.50	$36.50
Purchase #6	$30.31	11.372%	$33.7569	$33.76	$33.75	$33.80
Purchase #7	$199.51	11.322%	$222.0985	$222.10	$222.10	$222.10
7 purchase totals =	$934.03		$1,022.2970	$1,022.30	$1,022.30	$1,022.40