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	$247.77	13.253%	$280.607	$280.61	$280.60	$280.60
Purchase #2	$67.29	8.499%	$73.009	$73.01	$73.00	$73.00
Purchase #3	$248.49	12.758%	$280.1924	$280.19	$280.20	$280.20
Purchase #4	$250.63	5.160%	$263.5625	$263.56	$263.55	$263.60
Purchase #5	$23.40	9.475%	$25.6172	$25.62	$25.60	$25.60
Purchase #6	$192.69	11.223%	$214.3156	$214.32	$214.30	$214.30
Purchase #7	$80.70	5.802%	$85.3822	$85.38	$85.40	$85.40
7 purchase totals =	$1,110.97		$1,222.6859	$1,222.69	$1,222.65	$1,222.70