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	$81.54	9.732%	$89.4755	$89.48	$89.50	$89.50
Purchase #2	$66.90	8.758%	$72.7591	$72.76	$72.75	$72.80
Purchase #3	$112.45	11.570%	$125.4605	$125.46	$125.45	$125.50
Purchase #4	$5.96	10.679%	$6.5965	$6.60	$6.60	$6.60
Purchase #5	$187.37	9.143%	$204.5012	$204.50	$204.50	$204.50
Purchase #6	$112.37	6.705%	$119.9044	$119.90	$119.90	$119.90
Purchase #7	$127.46	12.577%	$143.4906	$143.49	$143.50	$143.50
7 purchase totals =	$694.05		$762.1878	$762.19	$762.20	$762.30