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	$93.78	4.111%	$97.6353	$97.64	$97.65	$97.60
Purchase #2	$126.57	9.826%	$139.0068	$139.01	$139.00	$139.00
Purchase #3	$233.82	3.802%	$242.7098	$242.71	$242.70	$242.70
Purchase #4	$78.55	13.758%	$89.3569	$89.36	$89.35	$89.40
Purchase #5	$68.71	5.481%	$72.476	$72.48	$72.50	$72.50
Purchase #6	$239.74	5.678%	$253.3524	$253.35	$253.35	$253.40
Purchase #7	$87.79	11.495%	$97.8815	$97.88	$97.90	$97.90
7 purchase totals =	$928.96		$992.4187	$992.43	$992.45	$992.50