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	$16.64	11.532%	$18.5589	$18.56	$18.55	$18.60
Purchase #2	$56.31	5.329%	$59.3108	$59.31	$59.30	$59.30
Purchase #3	$102.82	7.672%	$110.7084	$110.71	$110.70	$110.70
Purchase #4	$28.85	9.272%	$31.525	$31.53	$31.55	$31.50
Purchase #5	$208.84	7.185%	$223.8452	$223.85	$223.85	$223.80
Purchase #6	$8.72	3.325%	$9.0099	$9.01	$9.00	$9.00
Purchase #7	$194.83	13.724%	$221.5685	$221.57	$221.55	$221.60
7 purchase totals =	$617.01		$674.5267	$674.54	$674.50	$674.50