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	$119.69	3.542%	$123.9294	$123.93	$123.95	$123.90
Purchase #2	$99.35	10.280%	$109.5632	$109.56	$109.55	$109.60
Purchase #3	$239.62	13.287%	$271.4583	$271.46	$271.45	$271.50
Purchase #4	$216.98	3.726%	$225.0647	$225.06	$225.05	$225.10
Purchase #5	$35.55	13.617%	$40.3908	$40.39	$40.40	$40.40
Purchase #6	$125.55	7.310%	$134.7277	$134.73	$134.75	$134.70
Purchase #7	$245.75	13.350%	$278.5576	$278.56	$278.55	$278.60
7 purchase totals =	$1,082.49		$1,183.6917	$1,183.69	$1,183.70	$1,183.80