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	$183.43	3.794%	$190.3893	$190.39	$190.40	$190.40
Purchase #2	$226.77	13.357%	$257.0597	$257.06	$257.05	$257.10
Purchase #3	$84.59	8.253%	$91.5712	$91.57	$91.55	$91.60
Purchase #4	$37.85	13.222%	$42.8545	$42.85	$42.85	$42.90
Purchase #5	$157.27	5.218%	$165.4763	$165.48	$165.50	$165.50
Purchase #6	$61.31	12.833%	$69.1779	$69.18	$69.20	$69.20
Purchase #7	$114.42	3.618%	$118.5597	$118.56	$118.55	$118.60
7 purchase totals =	$865.64		$935.0886	$935.09	$935.10	$935.30