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	$176.44	5.162%	$185.5478	$185.55	$185.55	$185.50
Purchase #2	$25.62	9.524%	$28.06	$28.06	$28.05	$28.10
Purchase #3	$99.62	3.293%	$102.9005	$102.90	$102.90	$102.90
Purchase #4	$30.59	6.475%	$32.5707	$32.57	$32.55	$32.60
Purchase #5	$175.46	4.758%	$183.8084	$183.81	$183.80	$183.80
Purchase #6	$102.29	9.334%	$111.8377	$111.84	$111.85	$111.80
Purchase #7	$59.41	11.700%	$66.361	$66.36	$66.35	$66.40
7 purchase totals =	$669.43		$711.0861	$711.09	$711.05	$711.10